Biomass conversion systems having a fluid circulation loop containing backflushable filters for control of cellulosic fines and methods for use thereof

ABSTRACT

Digestion of cellulosic biomass to produce a hydrolysate may be accompanied by the formation of cellulosic fines which may be damaging to system components. Biomass conversion systems that may address the issue of cellulosic fines may comprise a fluid circulation loop comprising: a hydrothermal digestion unit; a solids separation unit that is in fluid communication with an outlet of the hydrothermal digestion unit; where the solids separation unit comprises a plurality of filters and the filters are in fluid communication with the fluid circulation loop in both a forward and a reverse flow direction; and a catalytic reduction reactor unit that is in fluid communication with an outlet of the solids separation unit and an inlet of the hydrothermal digestion unit; where at least one of the plurality of filters is in fluid communication with an inlet of the catalytic reduction reactor unit.

The present application claims the benefit of pending U.S. ProvisionalPatent Application Ser. No. 61/576,623 filed Dec. 16, 2011, the entiredisclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present disclosure generally relates to the processing of cellulosicbiomass solids using digestion to produce a hydrolysate, and, morespecifically, to biomass conversion systems and methods that allowcellulosic fines to be removed via filtration from a hydrolysateproduced during the digestion of cellulosic biomass solids.

BACKGROUND

Significant attention has been placed on developing alternative energysources to fossil fuels. One fossil fuel alternative having significantpotential is biomass, particularly cellulosic biomass such as, forexample, plant biomass. As used herein, the term “biomass” will refer toa living or recently living biological material. Complex organicmolecules within biomass can be extracted and broken down into simplerorganic molecules, which can subsequently be processed through knownchemical transformations into industrial chemicals or fuel blends (i.e.,a biofuel). In spite of biomass's potential in this regard, particularlyplant biomass, an energy- and cost-efficient process that enables theconversion of biomass into such materials has yet to be realized.

Cellulosic biomass is the world's most abundant source of carbohydratesdue to the lignocellulosic materials located within the cell walls ofhigher plants. Plant cell walls are divided into two sections: primarycell walls and secondary cell walls. The primary cell wall providesstructural support for expanding cells and contains three majorpolysaccharides (cellulose, pectin, and hemicellulose) and one group ofglycoproteins. The secondary cell wall, which is produced after the cellhas finished growing, also contains polysaccharides and is strengthenedthrough polymeric lignin covalently crosslinked to hemicellulose.Hemicellulose and pectin are typically found in abundance, but celluloseis the predominant polysaccharide and the most abundant source ofcarbohydrates. Collectively, these materials will be referred to hereinas “cellulosic biomass.”

Plants can store carbohydrates in forms such as, for example, sugars,starches, celluloses, lignocelluloses, and/or hemicelluloses. Any ofthese materials can represent a feedstock for conversion into industrialchemicals or fuel blends. Carbohydrates can include monosaccharidesand/or polysaccharides. As used herein, the term “monosaccharide” refersto hydroxy aldehydes or hydroxy ketones that cannot be furtherhydrolyzed to simpler carbohydrates. Examples of monosaccharides caninclude, for example, dextrose, glucose, fructose, and galactose. Asused herein, the term “polysaccharide” refers to saccharides comprisingtwo or more monosaccharides linked together by a glycosidic bond.Examples of polysaccharides can include, for example, sucrose, maltose,cellobiose, and lactose. Carbohydrates are produced duringphotosynthesis, a process in which carbon dioxide is converted intoorganic compounds as a way to store energy. This energy can be releasedwhen the carbohydrates are oxidized to generate carbon dioxide andwater.

Despite their promise, the development and implementation of bio-basedfuel technology has been slow. A number of reasons exist for this slowdevelopment. Ideally, a biofuel would be compatible with existing enginetechnology and have capability of being distributed through existingtransportation infrastructure. Current industrial processes for biofuelformation are limited to fermentation of sugars and starches to ethanol,which competes with these materials as a food source. In addition,ethanol has a low energy density when used as a fuel. Although somecompounds that have potential to serve as fuels can be produced frombiomass resources (e.g., ethanol, methanol, biodiesel, Fischer-Tropschdiesel, and gaseous fuels, such as hydrogen and methane), these fuelsgenerally require new distribution infrastructure and/or enginetechnologies to accommodate their physical characteristics. As notedabove, there has yet to be developed an industrially scalable processthat can convert biomass into fuel blends in a cost- andenergy-efficient manner that are similar to fossil fuels.

SUMMARY

The present disclosure generally relates to the processing of cellulosicbiomass solids using digestion to produce a hydrolysate, and, morespecifically, to biomass conversion systems and methods that allowcellulosic fines to be removed via filtration from a hydrolysateproduced during the digestion of cellulosic biomass solids.

In some embodiments, the present invention provides a method comprising:providing a biomass conversion system that comprises a fluid circulationloop comprising: a hydrothermal digestion unit; a solids separation unitthat is in fluid communication with an outlet of the hydrothermaldigestion unit; wherein the solids separation unit comprises a pluralityof filters; and a catalytic reduction reactor unit that is in fluidcommunication with an outlet of the solids separation unit and an inletof the hydrothermal digestion unit; providing a cellulosic biomass inthe hydrothermal digestion unit; at least partially digesting thecellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through at least one of thefilters to sequester the cellulosic fines; and backflushing at least aportion of the cellulosic fines to the hydrothermal digestion unit whilethe liquor phase continues to flow through one or more of the filters tothe catalytic reduction reactor unit.

In some embodiments, the present invention provides a method comprising:providing a biomass conversion system that comprises a fluid circulationloop comprising: a hydrothermal digestion unit; a solids separation unitthat is in fluid communication with an outlet of the hydrothermaldigestion unit; wherein the solids separation unit comprises a pluralityof filters; and a catalytic reduction reactor unit that is in fluidcommunication with an outlet of the solids separation unit and an inletof the hydrothermal digestion unit; providing a cellulosic biomass inthe hydrothermal digestion unit; at least partially digesting thecellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through at least one of thefilters to sequester the cellulosic fines; at least partially convertingthe soluble carbohydrates into a reaction product in the catalyticreduction reactor unit; and backflushing at least a portion of thecellulosic fines to the hydrothermal digestion unit using at least aportion of the reaction product.

In some embodiments, the present invention provides a biomass conversionsystem comprising: a fluid circulation loop comprising: a hydrothermaldigestion unit; a solids separation unit that is in fluid communicationwith an outlet of the hydrothermal digestion unit; wherein the solidsseparation unit comprises a plurality of filters; wherein the filtersare in fluid communication with the fluid circulation loop in both aforward and a reverse flow direction; and a catalytic reduction reactorunit that is in fluid communication with an outlet of the solidsseparation unit and an inlet of the hydrothermal digestion unit; whereinat least one of the plurality of filters is in fluid communication withan inlet of the catalytic reduction reactor unit.

The features and advantages of the present invention will be readilyapparent to one having ordinary skill in the art upon a reading of thedescription of the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent disclosure, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, as willoccur to one having ordinary in the art and the benefit of thisdisclosure.

FIG. 1 shows a schematic of an illustrative biomass conversion system inwhich parallel filters are used to sequester cellulosic fines.

FIG. 2 shows a schematic of an illustrative biomass conversion system inwhich a rotatable filter array is used to sequester cellulosic fines.

FIG. 3 shows a schematic of an illustrative biomass conversion system inwhich a hydroclone is used to remove cellulosic fines.

DETAILED DESCRIPTION

The present disclosure generally relates to the processing of cellulosicbiomass solids using digestion to produce a hydrolysate, and, morespecifically, to biomass conversion systems and methods that allowcellulosic fines to be removed via filtration from a hydrolysateproduced during the digestion of cellulosic biomass solids.

Unless otherwise specified herein, it is to be understood that use ofthe term “biomass” in the description that follows refers to “cellulosicbiomass solids.” Solids may be in any size, shape, or form. Thecellulosic biomass solids may be natively present in any of these solidsizes, shapes, or forms or may be further processed prior to digestionin the embodiments described herein. The cellulosic biomass solids maybe present in a slurry form in the embodiments described herein.

In practicing the present embodiments, any type of suitable biomasssource may be used. Suitable cellulosic biomass sources may include, forexample, forestry residues, agricultural residues, herbaceous material,municipal solid wastes, waste and recycled paper, pulp and paper millresidues, and any combination thereof. Thus, in some embodiments, asuitable cellulosic biomass may include, for example, corn stover,straw, bagasse, miscanthus, sorghum residue, switch grass, bamboo, waterhyacinth, hardwood, hardwood chips, hardwood pulp, softwood, softwoodchips, softwood pulp, and any combination thereof. Leaves, roots, seeds,stalks, and the like may be used as a source of the cellulosic biomass.Common sources of cellulosic biomass may include, for example,agricultural wastes (e.g., corn stalks, straw, seed hulls, sugarcaneleavings, nut shells, and the like), wood materials (e.g., wood or bark,sawdust, timber slash, mill scrap, and the like), municipal waste (e.g.,waste paper, yard clippings or debris, and the like), and energy crops(e.g., poplars, willows, switch grass, alfalfa, prairie bluestream,corn, soybeans, and the like). The cellulosic biomass may be chosenbased upon considerations such as, for example, cellulose and/orhemicellulose content, lignin content, growing time/season, growinglocation/transportation cost, growing costs, harvesting costs, and thelike.

When converting biomass into industrial chemicals and fuel blends, thecomplex organic molecules therein need to be broken down into simplermolecules, which may be transformed into other compounds. For cellulosicbiomass, the first step in this process is the production of solublecarbohydrates, typically by digestion. Digestion of cellulosic biomassmay be conducted using an acid or base in a kraft-like process at lowtemperatures and pressures to produce a biomass pulp. These types ofdigestion processes are commonly used in the paper and pulpwoodindustry. According to the embodiments described herein, the digestionrate of cellulosic biomass may be accelerated in the presence of adigestion solvent at elevated temperatures and pressures that maintainthe digestion solvent in a liquid state above its normal boiling point.In various embodiments, the digestion solvent may contain an organicsolvent, particularly an in situ-generated organic solvent, which mayprovide particular advantages, as described hereinafter.

When a digestion solvent is used at high temperatures and pressures, thedigestion process may become fairly energy intensive. If the energyinput requirements for the digestion process become too great, theeconomic feasibility of cellulosic biomass as a feedstock material maybe jeopardized. That is, if the energy input needed to digest cellulosicbiomass is too great, processing costs may become higher than the actualvalue of the product being generated. In order to keep processing costslow, the amount of externally added heat input to the digestion processshould be kept as low as possible while achieving as high as possibleconversion of the cellulosic biomass into soluble carbohydrates.

The present disclosure provides systems and methods that allowcellulosic biomass to be efficiently digested to form solublecarbohydrates, which may subsequently be converted through one or morecatalytic reduction reactions (e.g., hydrogenolysis and/orhydrogenation) into reaction products comprising oxygenatedintermediates that may be further processed into higher hydrocarbons.The higher hydrocarbons may be useful in forming industrial chemicalsand transportation fuels (i.e., a biofuel), including, for example,synthetic gasoline, diesel fuels, jet fuels, and the like. As usedherein, the term “biofuel” will refer to any transportation fuel formedfrom a biological source.

As used herein, the term “soluble carbohydrates” refers tomonosaccharides or polysaccharides that become solubilized in adigestion process. As used herein, the term “oxygenated intermediates”refers to alcohols, polyols, ketones, aldehydes, and mixtures thereofthat are produced from a catalytic reduction reaction (e.g.,hydrogenolysis and/or hydrogenation) of soluble carbohydrates. As usedherein, the term “higher hydrocarbons” refers to hydrocarbons having anoxygen to carbon ratio less than that of at least one component of thebiomass source from which they are produced. As used herein, the term“hydrocarbon” refers to an organic compound comprising primarilyhydrogen and carbon, although heteroatoms such as oxygen, nitrogen,sulfur, and/or phosphorus may be present in some embodiments. Thus, theterm “hydrocarbon” also encompasses heteroatom-substituted compoundscontaining carbon, hydrogen, and oxygen, for example.

Illustrative carbohydrates that may be present in cellulosic biomass mayinclude, for example, sugars, sugar alcohols, celluloses,lignocelluloses, hemicelluloses, and any combination thereof. Oncesoluble carbohydrates have been removed from the biomass matrix througha digestion process according to the embodiments described herein, thesoluble carbohydrates may be transformed into a reaction productcomprising oxygenated intermediates via a catalytic reduction reaction.Until the soluble carbohydrates are transformed by the catalyticreduction reaction, they are very reactive and may be subject todegradation under the digestion conditions. For example, solublecarbohydrates may degrade into insoluble byproducts such as, forexample, caramelans and other heavy ends degradation products that arenot readily transformable by further reactions into a biofuel. Suchdegradation products may also be harmful to equipment used in thebiomass processing. Thus, in some embodiments, the soluble carbohydratesand a digestion solvent may be circulated in a fluid circulation loop toremove them from the digestion conditions and convert them into lessreactive oxygenated intermediates via a catalytic reduction reaction.

In some embodiments, the oxygenated intermediates may be furthertransformed into a biofuel using any combination of furtherhydrogenolysis reactions, hydrogenation reactions, condensationreactions, isomerization reactions, oligomerization reactions,hydrotreating reactions, alkylation reactions, and the like. In someembodiments, at least a portion of the oxygenated intermediates may berecirculated to the hydrothermal digestion unit to comprise at least aportion of the digestion solvent. Recirculation of at least a portion ofthe oxygenated intermediates to the hydrothermal digestion unit may alsobe particularly advantageous in terms of heat integration and processefficiency.

A significant issue for processing cellulosic biomass is the developmentof a mechanism and process by which a pressurized hydrothermal digestionunit may be continuously or semi-continuously supplied with freshbiomass. Without the ability to introduce fresh biomass to a pressurizedhydrothermal digestion unit, depressurization and cooling of thehydrothermal digestion unit may take place during the addition of freshbiomass, significantly reducing the energy- and cost-efficiency of theconversion process. As used herein, the term “continuous addition” andgrammatical equivalents thereof will refer to a process in which biomassis added to a hydrothermal digestion unit in an uninterrupted mannerwithout fully depressurizing the hydrothermal digestion unit. As usedherein, the term “semi-continuous addition” and grammatical equivalentsthereof will refer to a discontinuous, but as-needed, addition ofbiomass to a hydrothermal digestion unit without fully depressurizingthe hydrothermal digestion unit.

A leading advantage of the biomass conversion systems described hereinis that the systems are designed to favor a high conversion of biomassinto soluble carbohydrates, which may be subsequently processed into abiofuel. The biomass conversion systems and associated methods describedherein are to be distinguished from those of the paper and pulpwoodindustry, where the goal is to harvest partially digested wood pulp,rather than obtaining as high as possible a quantity of solublecarbohydrates. In some embodiments, at least about 60% of the cellulosicbiomass, on a dry basis, may be digested to produce a hydrolysatecomprising soluble carbohydrates. In other embodiments, at least about90% of the cellulosic biomass, on a dry basis, may be digested toproduce a hydrolysate comprising soluble carbohydrates. The design ofthe present systems may enable such high conversion rates by minimizingthe formation of degradation products during the processing of biomass.

A significant issue that may be encountered when digesting cellulosicbiomass, particularly high conversion digestion to produce ahydrolysate, is that cellulosic fines may be produced within a liquorphase of the hydrolysate. As cellulosic biomass breaks apart duringdigestion, smaller and smaller particulates may be produced until onlyinsoluble materials remain. Cellulosic fines may also be present innative cellulosic biomass before digestion takes place. The cellulosicfines may still contain significant quantities of digestable cellulosematerials. The increasingly small cellulosic fines may remain inside thedigestion unit to undergo further digestion. A screen may be used at afluid exit of the digestion unit in order to assist in maintaining thecellulosic fines therein. At a certain size, the cellulosic fines maybecome so small that they are transported by liquor phase fluid flow. Ifthe cellulosic fines become sufficiently small, they may pass throughthe screen on the digestion unit and enter other portions of the biomassconversion system. As used herein, the term “cellulosic fines” willrefer to cellulosic biomass particles that are mobile in a liquor phaseand sufficiently small to pass through a screen. The cellulosic finesmay be of any shape and have a nominal size less than the nominal sizeof the biomass fed to the digestion unit. In some embodiments, thebiomass fed to the digestion unit may have a nominal particle sizeranging between about 0.5 inches and about 2 inches, with some particlesbeing 3 to 4 inches in size or larger. In some embodiments, cellulosicfines may be around 1 micron in size or smaller, more typically betweenabout 1 micron and about 100 microns. In some embodiments, cellulosicfines as large as about 1 mm may be transported out of the digestionunit via fluid flow.

Production of cellulosic fines may be particularly problematic from anoperational standpoint during the processing of cellulosic biomass.Cellulosic fines may plug fluid flow pathways in the biomass conversionsystems. They may be particularly deleterious to reactor units (e.g.,catalytic reduction reactor units used to reduce soluble carbohydratesinto oxygenated intermediates), where they may plug the reactor and/ordamage the catalyst. In addition, if not recovered and further digested,the cellulosic fines represent a lost source of cellulosic biomass thatremains unconverted into soluble carbohydrates for subsequenttransformation into other materials, particularly if they becomedeposited in a low temperature zone where further digestion does notproceed at an appreciable rate.

It is to be noted that production of cellulosic fines is not believed tobe problematic in biomass digestion processes in which the goal is toproduce biomass pulp, such as in kraft-type digestion in the paper andpulpwood industry. In digestion processes of these types, the digestionmay not proceed to a degree needed to reduce the biomass particulatesize sufficiently to produce cellulosic fines.

The present disclosure addresses the foregoing difficulty in the art byproviding a mechanism through which cellulosic fines may be removed froma liquor phase and subsequently returned to the digestion unit, ifdesired. The removal of cellulosic fines from the liquor phase and theirreturn to the digestion unit not only may protect the components of thebiomass conversion systems from particulate deposition damage, but italso may allow a greater percentage of the cellulosic biomass charge tobe digested to form a hydrolysate. If significant quantities of thecellulosic fines remain undigested, a lower yield of solublecarbohydrates may be obtained during digestion.

Another advantageous feature of the present biomass conversion systemsis that the removal and return of cellulosic fines to the digestion unitmay take place while high pressure digestion is occurring. That is, thedigestion unit may be operated continuously while cellulosic fines arebeing returned thereto, such that digestion may continue in asubstantially uninterrupted manner. This feature may improve the energyefficiency of the digestion process by not having to cool anddepressurize the digestion unit during fines removal or return. Itshould be noted, however, that in alternative embodiments, thecellulosic fines may be removed from the biomass conversion systems, ifdesired, and/or the return of cellulosic fines to the digestion unit maytake place while continuous digestion is not occurring.

As still another advantage, the present biomass conversion systems maybe configured such that fresh biomass may be continuously orsemi-continuously supplied to the digestion unit, such that thedigestion unit may operate continuously at elevated temperatures andpressures. That is, the biomass conversion systems may be configuredsuch that biomass may be added to a pressurized digestion system. Afurther description of biomass feed mechanisms that may supply biomassto a pressurized digestion unit are described in more detail below.

A further optional advantage of the present biomass conversion systemsinvolves operation of a solids separation unit therein at a temperaturesufficient to enable continued digestion of cellulosic fines to formsoluble carbohydrates and lignin. That is, the solids separation unitcan provide additional residence time for digestion of cellulosic fines.By allowing digestion to continue in the solids separation unit, fewerregeneration operations can be needed to remove and recover cellulosicfines. Further, the solids separation unit can be operated catalyticallyto enable some conversion of soluble carbohydrates to occur thereinbefore they are passed to a catalytic reduction reactor unit.

In some embodiments, biomass conversion systems described herein cancomprise:

a fluid circulation loop comprising: a hydrothermal digestion unit; asolids separation unit that is in fluid communication with an outlet ofthe hydrothermal digestion unit; wherein the solids separation unitcomprises a plurality of filters; wherein the filters are in fluidcommunication with the fluid circulation loop in both a forward and areverse flow direction; and a catalytic reduction reactor unit that isin fluid communication with an outlet of the solids separation unit andan inlet of the hydrothermal digestion unit; wherein at least one of theplurality of filters is in fluid communication with an inlet of thecatalytic reduction reactor unit. In such a configuration, at least oneof the filters can be backflushed to remove cellulosic fines therefrom,while one or more of the other filters remain in fluid communicationwith an inlet of the catalytic reduction reactor unit. That is, thefilters are configured such that they can be operated in a reciprocatingmanner in the embodiments described herein.

As used herein, the term “plurality of filters” refers to 2 or morefilters. In some embodiments, the plurality of filters may be connectedin parallel to one another. In other embodiments, the plurality offilters may be arranged on a rotatable filter array. In each of theseembodiments, at least one of the filters may be backflushed while fluidflow continues through at least one of the remaining filters in aforward flow direction. In such arrangements of the plurality offilters, the biomass conversion systems are capable of continuallyproducing a reaction product in the catalytic reduction reactor unit. Itis to be noted that in some alternative embodiments, each of theplurality of filters may be backflushed at the same time, such thathydrolysate flow to the catalytic reduction reactor unit is interrupted.If performed for a short time, such a flow interruption may notsubstantially upset the biomass conversion process. In still anotheralternative configuration, a single filter may be used, with morefrequent backflushing taking place.

The plurality of filters used in the present embodiments may be of anytype capable of affecting separation of solids from a fluid phase.Suitable filters may include, for example, surface filters and depthfilters. Surface filters may include, for example, filter papers,membranes, porous solid media, and the like. Depth filters may include,for example, a column or plug of porous media designed to trap solidswithin its core structure.

In some embodiments, the fluid circulation loop may be configured toestablish countercurrent flow in the hydrothermal digestion unit. Asused herein, the term “countercurrent flow” refers to the direction areaction product enters the hydrothermal digestion unit relative to thedirection in which biomass is introduced to the digestion unit. Otherflow configurations such as, for example, co-current flow may also beused, if desired. In some embodiments, at least one of the plurality offilters may be in fluid communication with an outlet of the catalyticreduction reactor unit. In such embodiments, at least a portion of areaction product produced in the catalytic reduction reactor unit may beused to backflush the one or more filters of the solids separation unit.

In some embodiments, at least one of the filters of the solidsseparation unit may comprise a catalytic filter. Such catalytic filtersmay comprise a solid support and a catalyst on the solid support. Forexample, in some embodiments, the solid support may comprise one or moreof the foregoing types of filtration media. In general, any type ofheterogeneous catalyst may be deposited on the solid support. In someembodiments, the catalyst on the solid support may be capable ofactivating molecular hydrogen. As described hereinafter, such catalystsmay be used to transform soluble carbohydrates into a reaction productcomprising oxygenated intermediates in the catalytic reduction reactorunit. For example, such catalysts may be used to perform ahydrogenolysis and/or hydrogenation reaction of the solublecarbohydrates by supplying molecular hydrogen to the filters. Byincluding a catalyst on at least one of the filters, a greater effectivetransformation of soluble carbohydrates into a reaction product may berealized. As a further advantage, by operating the filters at anelevated temperature, the filters may be made to be “self-healing”whereby materials plugging the filter may be further digested to producesoluble carbohydrates and reduce the frequency needed for filterregeneration.

In some embodiments, the hydrothermal digestion unit may be, forexample, a pressure vessel of carbon steel, stainless steel, or asimilar alloy. In some embodiments, a single hydrothermal digestion unitmay be used. In other embodiments, multiple hydrothermal digestion unitsoperating in series, parallel or any combination thereof may be used. Insome embodiments, digestion may be conducted in a pressurizedhydrothermal digestion unit operating continuously. However, in otherembodiments, digestion may be conducted in batch mode. Suitablehydrothermal digestion units may include, for example, the “PANDIA™Digester” (Voest-Alpine Industrienlagenbau GmbH, Linz, Austria), the“DEFIBRATOR Digester” (Sunds Defibrator AB Corporation, Stockholm,Sweden), the M&D (Messing & Durkee) digester (Bauer Brothers Company,Springfield, Ohio, USA) and the KAMYR Digester (Andritz Inc., GlensFalls, N.Y., USA). In some embodiments, the biomass may be at leastpartially immersed in the hydrothermal digestion unit. In otherembodiments, the hydrothermal digestion unit may be operated as atrickle bed or pile-type hydrothermal digestion unit. Fluidized bed andstirred contact hydrothermal digestion units may also be used in someembodiments. Suitable hydrothermal digestion unit designs may include,for example, co-current, countercurrent, stirred tank, or fluidized bedhydrothermal digestion units.

In general, digestion may be conducted in a liquor phase. In someembodiments, the liquor phase may comprise a digestion solvent thatcomprises water. In some embodiments, the liquor phase may furthercomprise an organic solvent. In some embodiments, the organic solventmay comprise oxygenated intermediates produced from a catalyticreduction reaction of soluble carbohydrates. For example, in someembodiments, a digestion solvent may comprise oxygenated intermediatesproduced by a hydrogenolysis reaction or other catalytic reductionreaction of soluble carbohydrates. In some embodiments, bio-ethanol maybe added to water as a startup digestion solvent, with a solventcomprising oxygenated intermediates being produced thereafter. Any otherorganic solvent that is miscible with water may also be used as astartup digestion solvent, if desired. In general, a sufficient amountof liquor phase is present in the digestion process such that thebiomass surface remains wetted. The amount of liquor phase may befurther chosen to maintain a sufficiently high concentration of solublecarbohydrates to attain a desirably high reaction rate during subsequentcatalytic reduction, but not so high such that degradation becomesproblematic. In some embodiments, the concentration of solublecarbohydrates may be kept below about 5% by weight of the liquor phaseto minimize degradation. However, it is to be recognized that higherconcentrations may be used in some embodiments. In some embodiments,organic acids such as, for example, acetic acid, oxalic acid,acetylsalicylic acid, and acetylsalicylic acid may be included in theliquor phase as an acid promoter of the digestion process.

In some embodiments, prior to digestion, the cellulosic biomass may bewashed and/or reduced in size (e.g., by chopping, crushing, debarking,and the like) to achieve a desired size and quality for being digested.The operations may remove substances that interfere with furtherchemical transformation of soluble carbohydrates and/or improve thepenetration of digestion solvent into the biomass. In some embodiments,washing may occur within the hydrothermal digestion unit prior topressurization. In other embodiments, washing may occur before thebiomass is placed in the hydrothermal digestion unit.

In some embodiments, the digestion solvent may comprise oxygenatedintermediates of an in situ generated organic solvent. As used herein,the term “in situ generated organic solvent” refers to the reactionproduct produced from a catalytic reduction reaction of solublecarbohydrates, where the catalytic reduction reaction takes place in acatalytic reduction reactor unit coupled to the biomass conversionsystem. In some embodiments, the in situ generated organic solvent maycomprise at least one alcohol, ketone, or polyol. In alternativeembodiments, the digestion solvent may be at least partially suppliedfrom an external source. For example, in an embodiment, bio-ethanol maybe used to supplement the in situ-generated organic solvent. Otherwater-miscible organic solvents may be used as well. In someembodiments, the digestion solvent may be separated, stored, orselectively injected into the hydrothermal digestion unit so as tomaintain a desired concentration of soluble carbohydrates.

In some embodiments, digestion may take place over a period of time atelevated temperatures and pressures. In some embodiments, digestion maytake place at a temperature ranging between about 100° C. to about 240°C. for a period of time. In some embodiments, the period of time mayrange between about 0.25 hours and about 24 hours. In some embodiments,the digestion to produce soluble carbohydrates may occur at a pressureranging between about 1 bar (absolute) and about 100 bar.

In various embodiments, suitable biomass digestion techniques mayinclude, for example, acid digestion, alkaline digestion, enzymaticdigestion, and digestion using hot-compressed water.

Various factors may influence the digestion process. In someembodiments, hemicellulose may be extracted from the biomass attemperatures below about 160° C. to produce a predominantly C₅carbohydrate fraction. At increasing temperatures, this C₅ carbohydratefraction may be thermally degraded. It may therefore be advantageous toconvert the C₅ and/or C₆ carbohydrates and/or other sugar intermediatesinto more stable intermediates such as sugar alcohols, alcohols, andpolyols. By reacting the soluble carbohydrates in a catalytic reductionreactor unit and recycling at least a portion of the reaction product tothe hydrothermal digestion unit, the concentration of oxygenatedintermediates may be increased to commercially viable concentrationswhile the concentration of soluble carbohydrates is kept low.

In some embodiments, cellulose digestion may begin above about 160° C.,with solubilization becoming complete at temperatures around about 190°C., aided by organic acids (e.g., carboxylic acids) formed from partialdegradation of carbohydrate components. Some lignins may be solubilizedbefore cellulose, while other lignins may persist to highertemperatures. These lignins may optionally be removed at a later time.The digestion temperature may be chosen so that carbohydrates aresolubilized while limiting the formation of degradation products.

In some embodiments, a plurality of hydrothermal digestion units may beused. In such embodiments, the biomass may first be introduced into ahydrothermal digestion unit operating at about 160° C. or below tosolubilize C₅ carbohydrates and some lignin without substantiallydegrading these products. The remaining biomass may then exit the firsthydrothermal digestion unit and pass to a second hydrothermal digestionunit. The second hydrothermal digestion unit may be used to solubilizeC₆ carbohydrates at a higher temperature. In another embodiment, aseries of hydrothermal digestion units may be used with an increasingtemperature profile so that a desired carbohydrate fraction issolubilized in each.

In some embodiments, the biomass conversion systems may further comprisea biomass feed mechanism that is operatively coupled to the hydrothermaldigestion unit and allows a cellulosic biomass to be continuously orsemi-continuously added to the hydrothermal digestion unit without thehydrothermal digestion unit being fully depressurized. In someembodiments, the biomass feed mechanism may comprise a pressurizationzone. Cellulosic biomass may be pressurized using the pressurizationzone and then introduced to the hydrothermal digestion unit in acontinuous or semi-continuous manner without fully depressurizing thedigestion unit. Pressurizing the cellulosic biomass prior to itsintroduction to the hydrothermal digestion unit may allow the digestionunit to remain pressurized and operating continuously during biomassaddition. Additional benefits of pressurizing the biomass prior todigestion are also discussed hereinafter. As used herein, the term“continuous addition” and grammatical equivalents thereof will refer toa process in which biomass is added to a digestion unit in anuninterrupted manner without fully depressurizing the digestion unit. Asused herein, the term “semi-continuous addition” and grammaticalequivalents thereof will refer to a discontinuous, but as-needed,addition of biomass to a digestion unit without fully depressurizing thedigestion unit.

In some embodiments, the biomass conversion systems may further comprisea loading mechanism that is operatively connected to the pressurizationzone. Any type of loading mechanism capable of dropping or transportingcellulosic biomass may be used in the present embodiments. Suitableloading mechanisms may include, for example, conveyer belts, vibrationaltube conveyers, screw feeders or conveyers, bin dispensers, and thelike. It is to be recognized that in some embodiments, the loadingmechanism may be omitted. For example, in some embodiments, addition ofcellulosic biomass to the pressurization zone may take place manually.In some embodiments, the cellulosic biomass may be provided andintroduced to the pressurization zone at the same time. That is, aloading mechanism need not necessarily be used.

During the operation of the biomass conversion systems, thepressurization zone may cycle between a pressurized state and an atleast partially depressurized state, while the hydrothermal digestionunit remains continuously operating in a pressurized state. While thepressurization zone is at least partially depressurized, cellulosicbiomass may be introduced to the pressurization zone via the loadingmechanism, if used. Suitable types of pressurization zones and operationthereof are described in commonly owned U.S. Patent Applications Ser.Nos. 61/576,664 and 61/576,691, each filed concurrently herewith andincorporated herein by reference in its entirety.

In some embodiments, the cellulosic biomass within the pressurizationzone may be pressurized, at least in part, by introducing at least aportion of the liquor phase in the hydrothermal digestion unit to thepressurization zone. In some or other embodiments, the cellulosicbiomass within the pressurization zone may be pressurized, at least inpart, by introducing a gas to the pressurization zone. In someembodiments, the liquor phase may comprise an organic solvent, which isgenerated as a reaction product of the catalytic reduction reactor unit.In other embodiments, an external solvent may be used to pressurize thepressurization zone.

At least two benefits may be realized by pressurizing the biomass in thepresence of the liquor phase from the hydrothermal digestion unit.First, pressurizing the biomass in the presence of the liquor phase maycause the digestion solvent to infiltrate the biomass, which causes thebiomass to sink in the digestion solvent once introduced to thedigestion solvent. Further, by adding hot liquor phase to the biomass inthe pressurization zone, less energy needs to be input to bring thebiomass up to temperature once introduced to the hydrothermal digestionunit. Both of these features may improve the efficiency of the digestionprocess.

In some embodiments, the present biomass conversion systems may furthercomprise a phase separation mechanism in fluid communication with anoutlet of the catalytic reduction reactor unit. Suitable phaseseparation mechanisms may include for, example, phase separation,solvent stripping columns, extractors, filters, distillations and thelike. In an embodiment, azeotropic distillation may be conducted. Insome embodiments, the phase separation mechanism may be used to separatean aqueous phase and an organic phase of the reaction product. In someembodiments, at least a portion of the aqueous phase may be recirculatedto the hydrothermal digestion unit and/or be used to transportcellulosic fines back to the digestion unit. In some or otherembodiments, at least a portion of the organic phase may be removed fromthe fluid circulation loop and subsequently be converted into a biofuel,as described hereinafter. In some embodiments, at least a portion of theorganic phase may be recirculated to the digestion unit.

The biomass conversion systems of the foregoing description will now befurther described with reference to the drawings. FIG. 1 shows aschematic of an illustrative biomass conversion system 1 in whichparallel filters are used to sequester cellulosic fines. Biomassconversion system 1 contains hydrothermal digestion unit 2, solidsseparation unit 10, and catalytic reduction reactor unit 4, whichtogether comprise fluid circulation loop 6. Within solids separationunit 10 are contained filters 12 and 12′, one of which may bebackflushed to remove particulate matter while the other continuesoperating in a forward flow direction. Filters 12 and 12′ are in fluidcommunication with fluid circulation loop 6 in both the forward andreverse flow direction. Accordingly, filters 12 and 12′ are reversiblefilters and may be operated in a reciprocating manner. As used herein,the term “reciprocating filters” refers to two or more filters, whereone filter is operating in a forward flow direction and one filter isoperating in a reverse flow direction, and where the flow direction ofthe two filters is changed together. Although FIG. 1 has depicted onlytwo parallel filters, it is to be recognized that any number of parallelfilters greater than or equal to two may also be used in accordance withthe embodiments presented in FIG. 1. As described above, one filter maybe used in an alternative configuration, but this may result in aninterruption of liquor phase flow to catalytic reduction reactor unit 4.

The direction of fluid flow in biomass conversion system 1 is indicatedwith arrows in FIG. 1, where one of the parallel filters is beingbackflushed with reverse flow and one of the parallel filters continuesoperating with forward flow. It is to be recognized that, in someembodiments, both filters may be operating in a forward flow mode. Thatis, it is not necessarily the case that backflushing continually takesplace. In some embodiments, the parallel filters may be bypassed, and areaction product from catalytic reduction reactor unit 4 may berecirculated directly to hydrothermal digestion unit 2 by line 8.

Optional line 20 may be used to recirculate the liquor phase within thedigestion unit. Reasons why one would want to include line 20 mayinclude, for example, to maintain linear velocity of the liquor phase inthe digestion unit and/or to further manage the temperature profile indigestion unit 2. Optional line 22 may be used to transfer liquor phasefrom the digestion unit. For example, line 22 may be used to transferliquor phase from the digestion unit, where the liquor phase may atleast partially pressurize pressurization zone 5. Cellulosic biomass maybe supplied to pressurization zone 5 from loading mechanism 7 beforepressurizing and introduction of the pressurized biomass to hydrothermaldigestion unit 2.

In the operation of biomass conversion system 1, cellulosic biomasswithin hydrothermal digestion unit 2 may be at least partially digestedto produce a hydrolysate comprising soluble carbohydrates within aliquor phase. As described herein, hydrothermal digestion unit 2 may beoperated at elevated temperatures and pressures that facilitate thedigestion of the biomass. The liquor phase may then be transferred tosolids separation unit 10 via line 30. As greater quantities of thecellulosic biomass are digested, cellulosic fines may be present in theliquor phase of the hydrolysate.

Control of the liquor phase within solids separation unit 10 may becontrolled by various valves 21. The position of valves 21 in FIG. 1should be considered illustrative in nature and non-limiting, as othervalves may be present, fewer valves may be used, and/or valves may belocated in other positions. As depicted in FIG. 1, the valves areconfigured such that the liquor phase flows through filter 12 tocatalytic reduction reactor unit 4. Within catalytic reduction reactorunit 4, soluble carbohydrates may be transformed into a reactionproduct. In some embodiments, lignins may also be transformable into areaction product. For example, the soluble carbohydrates may undergo acatalytic reduction reaction (e.g., a hydrogenolysis and/orhydrogenation reaction) to produce a reaction product comprisingoxygenated intermediates. If desired, at least a portion of the reactionproduct may be used to backflush solids separation unit 10, where thereaction product enters solids separation unit 10 via line 32.Alternatively, solids separation unit 10 may be backflushed with asolvent from an external source. In still another alternativeconfiguration, line 8 may be used to transfer at least a portion of thereaction product back to hydrothermal digestion unit 2, while bypassingsolids separation unit 10. Fluid flow within lines 8 and 32 may beregulated with valves 23 and 25. Reaction product not recirculated tohydrothermal digestion unit 2 and/or solids separation unit 10 may beremoved by line 34 for further transformation into a biofuel or othermaterial.

The direction of biomass introduction into hydrothermal digestion unit 2and flow of bulk biomass therein is indicated by a dashed arrow.Cellulosic fines may flow upward in the flow of digestion solvent. Asdepicted in FIG. 1, line 37 of fluid circulation loop 6 is configuredsuch that countercurrent flow is established in hydrothermal digestionunit 2. It is to be recognized, however, that other flow configurationsmay be used, including co-current flow, by connecting line 37 to anotherpoint in hydrothermal digestion unit 2.

When valve 23 is open, the reaction product may reenter solidsseparation unit 10 via line 32 for backflushing at least one of theparallel filters. As depicted in FIG. 1, the reaction product in line 32may flow to filter 12′ in a reverse direction via lines 36 and 38. Whilefilter 12′ is being backflushed, liquor phase continues to flow throughfilter 12 to catalytic reduction reactor unit 4.

By backflushing filter 12′, cellulosic fines or other particulate matterthereon may be recirculated to hydrothermal digestion unit 2 via line37. Once the cellulosic fines have been removed from filter 12′, thedirection of fluid flow through this filter may then be reversed. Insome embodiments, after the fluid flow direction through filter 12′ hasbeen reversed, the fluid flow direction through filter 12 may also bechanged, and this filter may then be similarly backflushed. Inalternative embodiments, both filters 12 and 12′ may be flowed in theforward direction to feed catalytic reduction reactor unit 4 for atleast some period of time.

The decision to reverse the flow direction through the parallel filtersand backflush the cellulosic fines may take place in response to anytype of trigger event. In some embodiments, backflushing may take placeat a fixed time interval. In some embodiments, backflushing may takeplace if the forward fluid flow rate through the filters drops below apre-determined level. In some embodiments, backflushing may take placeif the pressure drop for a fixed fluid flow rate through the filterincreases above a designated value. In still other embodiments,backflushing may take place in response to the height of a filter cakedeposited on the filters. Reversal of the fluid flow direction may takeplace manually in some embodiments, automatically in some embodiments,or any combination thereof.

FIG. 2 shows a schematic of an illustrative biomass conversion system 50in which a rotatable filter array is used to sequester cellulosic fines.This biomass conversion system embodies many of the features describedin more detail above for FIG. 1, so they will be described only in briefin the description that follows. Biomass conversion system 50 containshydrothermal digestion unit 52, solids separation unit 53 containingrotatable filter array 54, and catalytic reduction reactor unit 56,which collectively comprise fluid circulation loop 58. Rotatable filterarray 54 contains filters 60, 60′, and 60″, at least one of which may bebackflushed with reverse fluid flow to remove particulate matter whileat least another one of which may continue operating with forward fluidflow. Although FIG. 2 has depicted only three filters within rotatablefilter array 54, it is to be recognized that any number of filtersgreater than or equal to two may employed in embodiments where arotatable filter array is used.

The direction of fluid flow is indicated with arrows in FIG. 2. Asdepicted in FIG. 2, liquor phase flows from hydrothermal digestion unit52 through line 80 to solids separation unit 53. Fluid flow continues inthe forward direction through filter 60′ to catalytic reduction reactorunit 56 while filter 60 is being backflushed with reverse fluid flow. Asdepicted in FIG. 2, filter 60″ is not in use. Although FIG. 2 hasdepicted only two filters being used at the same time, more than twofilters may be in simultaneous use, if desired. For example, bysplitting the fluid flow (not shown), more than one filter may be usedin the forward or reverse flow direction.

Once the liquor phase flows through filter 60′ to remove cellulosicfines on the filtration medium, the liquor phase flows to catalyticreduction reactor unit 56 to produce a reaction product comprisingoxygenated intermediates. As above, this reaction product may be used tobackflush solids separation unit 53 via line 62 and/or recirculated todigestion unit 52 via line 64. Valves 63 and 65 may be used to controlfluid flow within lines 62 and 64. The position of these valves shouldbe considered illustrative in nature, and other valves may be present,if desired. In alternative embodiments, an external solvent may be usedto backflush solids separation unit 53, if desired. Cellulosic fines onfilter 60 may be returned to digestion unit 52 via line 68. At least aportion of the reaction product may be removed from biomass conversionsystem 50 via line 66 and subjected to further chemical transformations.

In the embodiment depicted in FIG. 2, once a desired amount ofcellulosic fines have been removed from filter 60 by backflushing, thisfilter may be placed back into service by turning rotatable filter array54. Turning of rotatable filter array 54 places another filter (e.g.,filter 60″) in a position for backflushing. Turning of rotatable filterarray 54 in the opposite direction would place filter 60′ in a positionfor backflushing and place filter 60″ in the forward fluid flow. Asdescribed in more detail for FIG. 1, optional line 70 may be used torecirculate the liquor phase within the digestion unit, and optionalline 72 may be used to transfer liquor phase from the digestion unit.For example, the liquor phase may be used to at least partiallypressurize pressurization zone 71. Cellulosic biomass may be supplied topressurization zone 71 from loading mechanism 73 before pressurizing andintroduction of the pressurized biomass to hydrothermal digestion unit52. Likewise, line 68 may be configured such that countercurrent flow isestablished within hydrothermal digestion unit 52, where the directionof biomass introduction into digestion unit 52 and the flow of bulkbiomass therein is indicated by dashed arrows.

In some embodiments, methods for processing biomass are describedherein. In some embodiments, the methods can comprise: providing abiomass conversion system that comprises a fluid circulation loopcomprising: a hydrothermal digestion unit; a solids separation unit thatis in fluid communication with an outlet of the hydrothermal digestionunit; wherein the solids separation unit comprises a plurality offilters; and a catalytic reduction reactor unit that is in fluidcommunication with an outlet of the solids separation unit and an inletof the hydrothermal digestion unit; providing a cellulosic biomass inthe hydrothermal digestion unit; at least partially digesting thecellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through at least one of thefilters to sequester the cellulosic fines; and backflushing at least aportion of the cellulosic fines to the hydrothermal digestion unit whilethe liquor phase continues to flow through one or more of the filters tothe catalytic reduction reactor unit.

In some embodiments, methods for processing biomass can comprise:providing a biomass conversion system that comprises a fluid circulationloop comprising: a hydrothermal digestion unit; a solids separation unitthat is in fluid communication with an outlet of the hydrothermaldigestion unit; wherein the solids separation unit comprises a pluralityof filters; and a catalytic reduction reactor unit that is in fluidcommunication with an outlet of the solids separation unit and an inletof the hydrothermal digestion unit; providing a cellulosic biomass inthe hydrothermal digestion unit; at least partially digesting thecellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through at least one of thefilters to sequester the cellulosic fines; at least partially convertingthe soluble carbohydrates into a reaction product in the catalyticreduction reactor unit; and backflushing at least a portion of thecellulosic fines to the hydrothermal digestion unit using at least aportion of the reaction product.

In some embodiments, the methods may further comprise forming a reactionproduct in the catalytic reduction reactor unit. In some embodiments, atleast a portion of the reaction product produced in the catalyticreduction reactor unit may be used to backflush the cellulosic finessequestered on the filter. In other embodiments, an external solvent maybe used to backflush the cellulosic fines sequestered on the filter. Insome embodiments, at least a portion of the reaction product may berecirculated to the hydrothermal digestion unit without being used tobackflush a filter, if desired. Optionally, any hydrogen in the reactionproduct may be removed therefrom prior to being used to backflush thesolids separation unit and/or being recirculated to the hydrothermaldigestion unit.

In some embodiments, at least one of the plurality of filters maycomprise a catalytic filter that comprises a solid support and acatalyst that is capable of activating molecular hydrogen. In someembodiments, the methods may further comprise at least partiallyconverting soluble carbohydrates into a reaction product on thecatalytic filter. Particular advantages of such an approach have beendescribed hereinabove. In some embodiments, the soluble carbohydratesmay be further converted into a reaction product in the catalyticreduction reactor unit. In some embodiments, the hydrolysate may beconverted into a reaction product, which may subsequently be convertedinto a biofuel.

In some embodiments, the methods may further comprise reversing thedirection of fluid flow in at least some of the filters. As describedabove, reversing the direction of fluid flow may remove cellulosic finesfrom the filters. In some embodiments, the methods may comprisereversing a direction of fluid flow in the filters that are beingbackflushed, and reversing a direction of fluid flow in one or more ofthe other filters so as to backflush cellulosic fines therefrom. Forexample, a filter that was previously being backflushed may be flowed inthe forward direction and a filter that was previously being used tosequester cellulosic fines may be backflushed by reversing the directionof fluid flow.

Solids separation units comprising separation mechanisms other thanfilters may also be used in alternative embodiments of the presentdisclosure to affect removal of cellulosic fines from the liquor phasebeing produced from digestion. In some embodiments, at least oneliquid-solid settling tank may be used to separate the cellulosic finesfrom the liquor phase obtained from the hydrothermal digestion unit. Insome embodiments, a centrifuge may be used to separate cellulosic finesfrom the liquor phase. In some embodiments, a centripetal force-basedseparation mechanism may be used in place of the plurality of filtersused in the previously described embodiments. Such centripetalforce-based separation mechanisms are also commonly referred to in theart as centrifugal force-based separation mechanisms and/or vortex-basedseparation mechanisms. In the description that follows, the term“centripetal force-based separation mechanism” will be used forsimplicity, but it is to be understood that this term may also representa similar centrifugal force-based separation mechanism or vortex-basedseparation mechanism. In some embodiments, a suitable centripetalforce-based separation mechanism may comprise a hydroclone (also knownin the art as a hydrocyclone).

The design and operation of a hydroclone will be familiar to one havingordinary skill in the art. As one of ordinary skill in the art willrecognize, a hydroclone contains a fluid inlet in which asolids-containing fluid enters a chamber within the hydroclone. Once inthe chamber, the fluid and solids may undergo rotational motion, therebyresulting in at least partial separation of the solids from the fluidphase. The hydroclone may further contain separate outlets for the fluidphase and the separated solids. Since the solids are typically moredense than the fluid phase, the solids outlet is usually located at thebottom of the hydroclone and the fluid outlet is usually located at thetop.

Use of a hydroclone in place of a plurality of filters may presentparticular advantages in the present embodiments. Since solidsseparation takes place as part of the hydroclone's design, nobackflushing is needed to remove solids from the solids separation unit.This feature makes the biomass conversion systems operationally simpler.Further, since there are no moving parts in a hydroclone, the risk ofmechanical failure may be reduced. As in the embodiments where aplurality of filters are used in the solids separation unit, cellulosicfines may also be returned to the digestion unit in embodiments where ahydroclone is used as well.

In some embodiments, biomass conversion systems can comprise: a fluidcirculation loop comprising: a hydrothermal digestion unit; a solidsseparation unit that is in fluid communication with an outlet of thehydrothermal digestion unit; wherein the solids separation unitcomprises a centripetal force-based separation mechanism that comprisesa fluid outlet and a solids outlet; and a catalytic reduction reactorunit that is in fluid communication with the fluid outlet of thecentripetal force-based separation mechanism and an inlet of thehydrothermal digestion unit. In some embodiments, the centripetalforce-based separation mechanism may comprise a hydroclone.

In some cases, a centripetal force-based separation mechanism may notremove the smallest cellulosic fines from the liquor phase. In the eventthat the centripetal force-based separation mechanism fails to removeall the cellulosic fines, two or more centripetal force-based separationmechanisms may be used in series, or another secondary separationmechanism may be used after the centripetal force-based separationmechanism. For example, in some embodiments, at least one filter may bepresent between the solids separation unit and the catalytic reductionreactor unit. This filter may provide a secondary separation ofcellulosic fines before the liquor phase enters the catalytic reductionreactor unit.

In some embodiments, the biomass conversion systems may further comprisea solids collection unit that is operatively coupled to the solidsoutlet of the centripetal force-based separation mechanism. Cellulosicfines collected in the solids collection unit may either be discarded orpreferably returned to the hydrothermal digestion unit. In alternativeembodiments, the solids collection unit may be omitted, and the solidsoutlet of the centripetal force-based separation may be in directoperative coupling with the hydrothermal digestion unit or the fluidcirculation loop, such that separated cellulosic fines may be returnedto the hydrothermal digestion unit.

In some embodiments, the biomass conversion systems may further comprisea return line establishing fluid communication between the solidscollection unit and the fluid circulation loop. In some embodiments, areaction product produced in the catalytic reduction reactor unit may beused to transport the collected cellulosic fines to the hydrothermaldigestion unit. In other embodiments, an externally added solvent may beused to transport the cellulosic fines to the hydrothermal digestionunit. In some embodiments, the biomass conversion systems may furthercomprise a fluid transfer line that establishes fluid communicationbetween an outlet of the catalytic reduction reactor unit and a solidscollection unit.

In some embodiments, the fluid circulation loop of biomass conversionsystems containing a centripetal force-based separation mechanism may beconfigured to establish countercurrent flow in the hydrothermaldigestion unit. As described above, other flow configurations such as,for example, co-current flow may also be used.

In some embodiments, biomass conversion systems employing a centripetalforce-based separation mechanism may further comprise a phase separationmechanism in fluid communication with an outlet of the catalyticreduction reactor unit. Suitable phase separation mechanisms may includefor, example, phase separation, solvent stripping columns, extractors,filters, distillations and the like. In an embodiment, azeotropicdistillation may be conducted. In some embodiments, the phase separationmechanism may be used to separate an aqueous phase and an organic phaseof the reaction product. In some embodiments, at least a portion of theaqueous phase may be recirculated to the hydrothermal digestion unitand/or be used to transport cellulosic fines back to the digestion unit.In some or other embodiments, at least a portion of the organic phasemay be removed from the fluid circulation loop and subsequently beconverted into a biofuel, as described hereinafter. In some embodiments,at least a portion of the organic phase may be recirculated to thedigestion unit.

Embodiments of biomass conversion systems that utilize a hydroclone willnow be described in further detail with reference to the drawings. FIG.3 shows a schematic of an illustrative biomass conversion system 100 inwhich a hydroclone is used to remove cellulosic fines. Biomassconversion system 100 contains hydrothermal digestion unit 102, solidsseparation unit 110 which contains hydroclone 112, and catalyticreduction reactor unit 114, which together comprise fluid circulationloop 120. Optionally, secondary filter 118 may be present between solidsseparation unit 110 and catalytic reduction reactor unit 114. Hydroclone112 contains a fluid outlet that establishes fluid communication withcatalytic reduction reactor unit 114 via line 130. Hydroclone 112 alsocontains a solids outlet connected to line 132 that allows cellulosicfines to be removed from hydroclone 112. Although FIG. 3 has depictedonly a single hydroclone, it is to be recognized that any number ofhydroclones greater than or equal to one may also be used in the presentembodiments. For example, multiple hydroclones may be used in parallel,in series, or any combination thereof in order to achieve a desireddegree of cellulosic fines separation from a liquor phase obtained fromhydrothermal digestion unit 102.

A liquor phase containing hydrolysate may travel from hydrothermaldigestion unit 102 to hydroclone 112 via line 144. Once solidsseparation takes place in hydroclone 112, the hydrolysate then travelsto catalytic reduction reactor unit 114 via line 130. A reaction productmay be produced from soluble carbohydrates in the liquor phase incatalytic reduction reactor unit 114. At least a portion of thisreaction product may be recirculated to hydrothermal digestion unit 102via line 142, if desired. Reaction product not recirculated tohydrothermal digestion unit 102 may be removed via takeoff line 144 andthereafter be further converted into a biofuel.

Biomass conversion system 100 also may optionally contain solidscollection unit 140 in which cellulosic fines may collect once separatedin hydroclone 112. Cellulosic fines may travel to solids collection unit140 via line 132. In an alternative configuration (not shown), line 132may directly connect to hydrothermal digestion unit 102 or line 142 inorder to directly return the cellulosic fines. In some embodiments, atleast a portion of the reaction product produced in catalytic reductionreactor unit 114 may be used to transfer the collected cellulosic finesin solids collection unit 140 to hydrothermal digestion unit 102. Asdepicted in FIG. 3, a reaction product from catalytic reduction reactorunit 114 may enter solids collection unit 140 via line 150. The reactionproduct and cellulosic fines may then travel from solids collection unit140 via line 152, which reconnects with line 142. Alternatively, line152 may directly reconnect to hydrothermal digestion unit 102. In someembodiments, the reaction product may be continuously circulated throughsolids collection unit 140. In other embodiments, the reaction productmay be periodically circulated through solids collection unit 140, inwhich case the reaction product may flow directly back to hydrothermaldigestion unit 102 via line 142. Regulation and direction of thereaction product fluid flow may be performed using valves 151 and 153.The position of these valves should be considered illustrative innature, and other valves may be present, if desired.

As described in more detail for FIG. 1, optional line 160 may be used torecirculate the liquor phase within the digestion unit, and optionalline 162 may be used to transfer liquor phase from the digestion unit.For example, the liquor phase may be used to at least partiallypressurize pressurization zone 164. Cellulosic biomass may be suppliedto pressurization zone 164 from loading mechanism 166 beforepressurizing and introduction of the pressurized biomass to hydrothermaldigestion unit 102. Likewise, line 142 may be configured such thatcountercurrent flow is established within hydrothermal digestion unit102, where the direction of biomass introduction into hydrothermaldigestion unit 102 is indicated by a dashed arrow. As previouslydescribed, other flow configurations may also be used.

In some embodiments, the biomass conversion systems may be used for theprocessing of cellulosic biomass, as described above. In someembodiments, the methods can comprise: providing a biomass conversionsystem that comprises a fluid circulation loop comprising: ahydrothermal digestion unit; a solids separation unit that is in fluidcommunication with an outlet of the hydrothermal digestion unit; whereinthe solids separation unit comprises a centripetal force-basedseparation mechanism; and a catalytic reduction reactor unit that is influid communication with a fluid outlet of the solids separation unitand an inlet of the hydrothermal digestion unit; providing a cellulosicbiomass in the hydrothermal digestion unit; at least partially digestingthe cellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through the solids separationunit to remove at least a portion of the cellulosic fines; afterremoving at least a portion of the cellulosic fines, flowing the liquorphase to the catalytic reduction reactor unit and forming a reactionproduct in the catalytic reduction reactor unit; and recirculating atleast a portion of the reaction product to the hydrothermal digestionunit.

In some embodiments, the methods can comprise: providing a biomassconversion system that comprises a fluid circulation loop comprising: ahydrothermal digestion unit; a solids separation unit that is in fluidcommunication with an outlet of the hydrothermal digestion unit; whereinthe solids separation unit comprises a centripetal force-basedseparation mechanism; and a catalytic reduction reactor unit that is influid communication with a fluid outlet of the solids separation unitand an inlet of the hydrothermal digestion unit; providing a cellulosicbiomass in the hydrothermal digestion unit; at least partially digestingthe cellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through the solids separationunit to remove at least a portion of the cellulosic fines; afterremoving at least a portion of the cellulosic fines, flowing the liquorphase to the catalytic reduction reactor unit and forming a reactionproduct in the catalytic reduction reactor unit; collecting thecellulosic fines in a solids collection unit; and transferring at leasta portion of the collected cellulosic fines to the hydrothermaldigestion unit using at least a portion of the reaction product.

In the various embodiments described herein, the hydrothermal digestionunit may typically be maintained at a pressure of at least about 30 barto ensure that digestion takes place at a desired rate. In someembodiments, the hydrothermal digestion unit may be maintained at apressure ranging between about 30 bar and about 430 bar. In someembodiments, the hydrothermal digestion unit may be maintained at apressure ranging between about 50 bar and about 330 bar. In someembodiments, the hydrothermal digestion unit may be maintained at apressure ranging between about 70 bar and about 130 bar. In still otherembodiments, the hydrothermal digestion unit may be maintained at apressure ranging between about 30 bar and about 130 bar. It is to benoted that the foregoing pressures refer to the pressures at whichdigestion takes place. That is, the foregoing pressures refer to normaloperating pressures for the hydrothermal digestion unit.

In some embodiments, the methods described herein may further compriseconverting the hydrolysate into a biofuel. In some embodiments,conversion of the hydrolysate into a biofuel may begin with a catalytichydrogenolysis reaction to transform soluble carbohydrates produced fromdigestion into a reaction product comprising oxygenated intermediates,as described above. As described above and depicted in FIGS. 1-3, thereaction product may be recirculated to the hydrothermal digestion unitto further aid in the digestion process. The reaction product may alsobe used to transfer return cellulosic fines to the digestion unit forfurther digestion. In some embodiments, the reaction product may befurther transformed by any number of further catalytic reformingreactions including, for example, further catalytic reduction reactions(e.g., hydrogenolysis reactions, hydrogenation reactions, hydrotreatingreactions, and the like), condensation reactions, isomerizationreactions, desulfurization reactions, dehydration reactions,oligomerization reactions, alkylation reactions, and the like. Adescription of the initial hydrogenolysis reaction and the furthercatalytic reforming reactions are described hereinafter.

Various processes are known for performing hydrogenolysis ofcarbohydrates. One suitable method includes contacting a carbohydrate orstable hydroxyl intermediate with hydrogen, optionally mixed with adiluent gas, and a hydrogenolysis catalyst under conditions effective toform a reaction product comprising oxygenated intermediates such as, forexample, smaller molecules or polyols. As used herein, the term “smallermolecules or polyols” includes any molecule that having a lowermolecular weight, which may include a smaller number of carbon atoms oroxygen atoms, than the starting carbohydrate. In an embodiment, thereaction products may include smaller molecules such as, for example,polyols and alcohols. This aspect of hydrogenolysis entails the breakingof carbon-carbon bonds

In an embodiment, a soluble carbohydrate may be converted to relativelystable oxygenated intermediates such as, for example, propylene glycol,ethylene glycol, and glycerol using a hydrogenolysis reaction in thepresence of a catalyst that is capable of activating molecular hydrogen.Suitable catalysts may include, for example, Cr, Mo, W, Re, Mn, Cu, Cd,Fe, Co, Ni, Pt, Pd, Rh, Ru, Ir, Os, and alloys or any combinationthereof, either alone or with promoters such as Au, Ag, Cr, Zn, Mn, Sn,Bi, B, O, and alloys or any combination thereof. In some embodiments,the catalysts and promoters may allow for hydrogenation andhydrogenolysis reactions to occur at the same time or in succession,such as the hydrogenation of a carbonyl group to form an alcohol. Thecatalyst may also include a carbonaceous pyropolymer catalyst containingtransition metals (e.g., chromium, molybdenum, tungsten, rhenium,manganese, copper, and cadmium) or Group VIII metals (e.g., iron,cobalt, nickel, platinum, palladium, rhodium, ruthenium, iridium, andosmium). In certain embodiments, the catalyst may include any of theabove metals combined with an alkaline earth metal oxide or adhered to acatalytically active support. In certain embodiments, the catalystdescribed in the hydrogenolysis reaction may include a catalyst support.

The conditions for which to carry out the hydrogenolysis reaction willvary based on the type of biomass starting material and the desiredproducts (e.g. gasoline or diesel), for example. One of ordinary skillin the art, with the benefit of this disclosure, will recognize theappropriate conditions to use to carry out the reaction. In general, thehydrogenolysis reaction may be conducted at temperatures in the range ofabout 110° C. to about 300° C., and preferably from about 170° C. toabout 300° C., and most preferably from about 180° C. to about 290° C.

In an embodiment, the hydrogenolysis reaction may be conducted underbasic conditions, preferably at a pH of about 8 to about 13, and evenmore preferably at a pH of about 10 to about 12. In an embodiment, thehydrogenolysis reaction may be conducted at a pressure ranging betweenabout 1 bar (absolute) and about 150 bar, and preferably at a pressureranging between about 15 bar and about 140 bar, and even more preferablyat a pressure ranging between 50 bar and 110 bar.

The hydrogen used in the hydrogenolysis reaction may include externalhydrogen, recycled hydrogen, in situ generated hydrogen, or anycombination thereof.

In some embodiments, the reaction products of the hydrogenolysisreaction may comprise greater than about 25% by mole, or alternatively,greater than about 30% by mole of polyols, which may result in a greaterconversion to a biofuel in a subsequent processing reaction.

In some embodiments, hydrogenolysis may be conducted under neutral oracidic conditions, as needed to accelerate hydrolysis reactions inaddition to the hydrogenolysis reaction. For example, hydrolysis ofoligomeric carbohydrates may be combined with hydrogenation to producesugar alcohols, which may undergo hydrogenolysis.

A second aspect of hydrogenolysis entails the breaking of —OH bonds suchas: RC(H)₂—OH+H₂→RCH₃+H₂O. This reaction is also called“hydrodeoxygenation,” and may occur in parallel with C—C bond breakinghydrogenolysis. Diols may be converted to mono-oxygenates via thisreaction. As reaction severity is increased with increased temperatureor contact time with catalyst, the concentration of polyols and diolsrelative to mono-oxygenates may diminish as a result ofhydrodeoxygenation. Selectivity for C—C vs. C—OH bond hydrogenolysiswill vary with catalyst type and formulation. Full de-oxygenation toalkanes may also occur, but is generally undesirable if the intent is toproduce mono-oxygenates or diols and polyols which may be condensed oroligomerized to higher molecular weight compounds in a subsequentprocessing step. Typically, it is desirable to send only mono-oxygenatesor diols to subsequent processing steps, as higher polyols may lead toexcessive coke formation during condensation or oligomerization.Alkanes, in contrast, are essentially unreactive and cannot be readilycombined to produce higher molecular compounds.

Once oxygenated intermediates have been formed by a hydrogenolysisreaction, a portion of the reaction product may be recirculated to thehydrothermal digestion unit to serve as an internally generateddigestion solvent. Another portion of the reaction product may bewithdrawn and subsequently processed by further reforming reactions toform a biofuel. Before being subjected to the further reformingreactions, the oxygenated intermediates may optionally be separated intodifferent components. Suitable separations may include, for example,phase separation, solvent stripping columns, extractors, filters,distillations and the like. In some embodiments, a separation of ligninfrom the oxygenated intermediates before the reaction product issubsequently processed further or recirculated to the hydrothermaldigestion unit.

The oxygenated intermediates may be processed to produce a fuel blend inone or more processing reactions. In an embodiment, a condensationreaction may be used along with other reactions to generate a fuel blendand may be catalyzed by a catalyst comprising an acid, a base, or both.In general, without being limited to any particular theory, it isbelieved that the basic condensation reactions may involve a series ofsteps involving: (1) an optional dehydrogenation reaction; (2) anoptional dehydration reaction that may be acid catalyzed; (3) an aldolcondensation reaction; (4) an optional ketonization reaction; (5) anoptional furanic ring opening reaction; (6) hydrogenation of theresulting condensation products to form a ≧C₄ hydrocarbon; and (7) anycombination thereof. Acid catalyzed condensations may similarly entailoptional hydrogenation or dehydrogenation reactions, dehydration, andoligomerization reactions. Additional polishing reactions may also beused to conform the product to a specific fuel standard, includingreactions conducted in the presence of hydrogen and a hydrogenationcatalyst to remove functional groups from final fuel product. In someembodiments, a basic catalyst, a catalyst having both an acid and a basefunctional site, and optionally comprising a metal function, may also beused to effect the condensation reaction.

In some embodiments, an aldol condensation reaction may be used toproduce a fuel blend meeting the requirements for a diesel fuel or jetfuel. Traditional diesel fuels are petroleum distillates rich inparaffinic hydrocarbons. They have boiling ranges as broad as 187° C. to417° C., which are suitable for combustion in a compression ignitionengine, such as a diesel engine vehicle. The American Society of Testingand Materials (ASTM) establishes the grade of diesel according to theboiling range, along with allowable ranges of other fuel properties,such as cetane number, cloud point, flash point, viscosity, anilinepoint, sulfur content, water content, ash content, copper stripcorrosion, and carbon residue. Thus, any fuel blend meeting ASTM D975may be defined as diesel fuel.

The present disclosure also provides methods to produce jet fuel. Jetfuel is clear to straw colored. The most common fuel is anunleaded/paraffin oil-based fuel classified as Aeroplane A-1, which isproduced to an internationally standardized set of specifications. Jetfuel is a mixture of a large number of different hydrocarbons, possiblyas many as a thousand or more. The range of their sizes (molecularweights or carbon numbers) is restricted by the requirements for theproduct, for example, freezing point or smoke point. Kerosene-typeAirplane fuel (including Jet A and Jet A-1) has a carbon numberdistribution between about C₈ and C₁₆. Wide-cut or naphtha-type Airplanefuel (including Jet B) typically has a carbon number distributionbetween about C₅ and C₁₅. A fuel blend meeting ASTM D1655 may be definedas jet fuel.

In certain embodiments, both Airplanes (Jet A and Jet B) contain anumber of additives. Useful additives include, but are not limited to,antioxidants, antistatic agents, corrosion inhibitors, and fuel systemicing inhibitor (FSII) agents. Antioxidants prevent gumming and usually,are based on alkylated phenols, for example, AO-30, AO-31, or AO-37.Antistatic agents dissipate static electricity and prevent sparking.Stadis 450 with dinonylnaphthylsulfonic acid (DINNSA) as the activeingredient, is an example. Corrosion inhibitors (e.g., DCI-4A) are usedfor civilian and military fuels, and DCI-6A is used for military fuels.FSII agents, include, for example, Di-EGME.

In some embodiments, the oxygenated intermediates may comprise acarbonyl-containing compound that may take part in a base catalyzedcondensation reaction. In some embodiments, an optional dehydrogenationreaction may be used to increase the amount of carbonyl-containingcompounds in the oxygenated intermediate stream to be used as a feed tothe condensation reaction. In these embodiments, the oxygenatedintermediates and/or a portion of the bio-based feedstock stream may bedehydrogenated in the presence of a catalyst.

In some embodiments, a dehydrogenation catalyst may be preferred for anoxygenated intermediate stream comprising alcohols, diols, and triols.In general, alcohols cannot participate in aldol condensation directly.The hydroxyl group or groups present may be converted into carbonyls(e.g., aldehydes, ketones, etc.) in order to participate in an aldolcondensation reaction. A dehydrogenation catalyst may be included toeffect dehydrogenation of any alcohols, diols, or polyols present toform ketones and aldehydes. The dehydration catalyst is typically formedfrom the same metals as used for hydrogenation, hydrogenolysis, oraqueous phase reforming. These catalysts are described in more detailabove. Dehydrogenation yields may be enhanced by the removal orconsumption of hydrogen as it forms during the reaction. Thedehydrogenation step may be carried out as a separate reaction stepbefore an aldol condensation reaction, or the dehydrogenation reactionmay be carried out in concert with the aldol condensation reaction. Forconcerted dehydrogenation and aldol condensation reactions, thedehydrogenation and aldol condensation functions may take place on thesame catalyst. For example, a metal hydrogenation/dehydrogenationfunctionality may be present on catalyst comprising a basicfunctionality.

The dehydrogenation reaction may result in the production of acarbonyl-containing compound. Suitable carbonyl-containing compounds mayinclude, but are not limited to, any compound comprising a carbonylfunctional group that may form carbanion species or may react in acondensation reaction with a carbanion species. In an embodiment, acarbonyl-containing compound may include, but is not limited to,ketones, aldehydes, furfurals, hydroxy carboxylic acids, and, carboxylicacids. Ketones may include, without limitation, hydroxyketones, cyclicketones, diketones, acetone, propanone, 2-oxopropanal, butanone,butane-2,3-dione, 3-hydroxybutane-2-one, pentanone, cyclopentanone,pentane-2,3-dione, pentane-2,4-dione, hexanone, cyclohexanone,2-methyl-cyclopentanone, heptanone, octanone, nonanone, decanone,undecanone, dodecanone, methylglyoxal, butanedione, pentanedione,diketohexane, dihydroxyacetone, and isomers thereof. Aldehydes mayinclude, without limitation, hydroxyaldehydes, acetaldehyde,glyceraldehyde, propionaldehyde, butyraldehyde, pentanal, hexanal,heptanal, octanal, nonal, decanal, undecanal, dodecanal, and isomersthereof. Carboxylic acids may include, without limitation, formic acid,acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoicacid, heptanoic acid, isomers and derivatives thereof, includinghydroxylated derivatives, such as 2-hydroxybutanoic acid and lacticacid. Furfurals may include, without limitation, hydroxylmethylfurfural,5-hydroxymethyl-2(5H)-furanone,dihydro-5-(hydroxymethyl)-2(3H)-furanone, tetrahydro-2-furoic acid,dihydro-5-(hydroxymethyl)-2(3H)-furanone, tetrahydrofurfuryl alcohol,1-(2-furyl)ethanol, hydroxymethyltetrahydrofurfural, and isomersthereof. In an embodiment, the dehydrogenation reaction may result inthe production of a carbonyl-containing compound that is combined withthe oxygenated intermediates to become a part of the oxygenatedintermediates fed to the condensation reaction.

In an embodiment, an acid catalyst may be used to optionally dehydrateat least a portion of the oxygenated intermediate stream. Suitable acidcatalysts for use in the dehydration reaction may include, but are notlimited to, mineral acids (e.g., HCl, H₂SO₄), solid acids (e.g.,zeolites, ion-exchange resins) and acid salts (e.g., LaCl₃). Additionalacid catalysts may include, without limitation, zeolites, carbides,nitrides, zirconia, alumina, silica, aluminosilicates, phosphates,titanium oxides, zinc oxides, vanadium oxides, lanthanum oxides, yttriumoxides, scandium oxides, magnesium oxides, cerium oxides, barium oxides,calcium oxides, hydroxides, heteropolyacids, inorganic acids, acidmodified resins, base modified resins, and any combination thereof. Insome embodiments, the dehydration catalyst may also include a modifier.Suitable modifiers may include, for example, La, Y, Sc, P, B, Bi, Li,Na, K, Rb, Cs, Mg, Ca, Sr, Ba, and any combination thereof. Themodifiers may be useful, inter alia, to carry out a concertedhydrogenation/dehydrogenation reaction with the dehydration reaction. Insome embodiments, the dehydration catalyst may also include a metal.Suitable metals may include, for example, Cu, Ag, Au, Pt, Ni, Fe, Co,Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, alloys, andany combination thereof. The dehydration catalyst may be selfsupporting, supported on an inert support or resin, or it may bedissolved in solution.

In some embodiments, the dehydration reaction may occur in the vaporphase. In other embodiments, the dehydration reaction may occur in theliquid phase. For liquid phase dehydration reactions, an aqueoussolution may be used to carry out the reaction. In an embodiment, othersolvents in addition to water, may be used to form the aqueous solution.For example, water soluble organic solvents may be present. Suitablesolvents may include, but are not limited to, hydroxymethylfurfural(HMF), dimethylsulfoxide (DMSO), 1-methyl-n-pyrollidone (NMP), and anycombination thereof. Other suitable aprotic solvents may also be usedalone or in combination with any of these solvents.

In an embodiment, the processing reactions may comprise an optionalketonization reaction. A ketonization reaction may increase the numberof ketone functional groups within at least a portion of the oxygenatedintermediates. For example, an alcohol may be converted into a ketone ina ketonization reaction. Ketonization may be carried out in the presenceof a basic catalyst. Any of the basic catalysts described above as thebasic component of the aldol condensation reaction may be used to effecta ketonization reaction. Suitable reaction conditions are known to oneof ordinary skill in the art and generally correspond to the reactionconditions listed above with respect to the aldol condensation reaction.The ketonization reaction may be carried out as a separate reactionstep, or it may be carried out in concert with the aldol condensationreaction. The inclusion of a basic functional site on the aldolcondensation catalyst may result in concerted ketonization and aldolcondensation reactions.

In an embodiment, the processing reactions may comprise an optionalfuranic ring opening reaction. A furanic ring opening reaction mayresult in the conversion of at least a portion of any oxygenatedintermediates comprising a furanic ring into compounds that are morereactive in an aldol condensation reaction. A furanic ring openingreaction may be carried out in the presence of an acidic catalyst. Anyof the acid catalysts described above as the acid component of the aldolcondensation reaction may be used to effect a furanic ring openingreaction. Suitable reaction conditions are known to one of ordinaryskill in the art and generally correspond to the reaction conditionslisted above with respect to the aldol condensation reaction. Thefuranic ring opening reaction may be carried out as a separate reactionstep, or it may be carried out in concert with the aldol condensationreaction. The inclusion of an acid functional site on the aldolcondensation catalyst may result in a concerted furanic ring openingreaction and aldol condensation reactions. Such an embodiment may beadvantageous as any furanic rings may be opened in the presence of anacid functionality and reacted in an aldol condensation reaction using abasic functionality. Such a concerted reaction scheme may allow for theproduction of a greater amount of higher hydrocarbons to be formed for agiven oxygenated intermediate feed.

In an embodiment, production of a ≧C₄ compound may occur bycondensation, which may include aldol condensation of the oxygenatedintermediates in the presence of a condensation catalyst.Aldol-condensation generally involves the carbon-carbon coupling betweentwo compounds, at least one of which may contain a carbonyl group, toform a larger organic molecule. For example, acetone may react withhydroxymethylfurfural to form a C₉ species, which may subsequently reactwith another hydroxymethylfurfural molecule to form a C₁₅ species. Invarious embodiments, the reaction is usually carried out in the presenceof a condensation catalyst. The condensation reaction may be carried outin the vapor or liquid phase. In an embodiment, the reaction may takeplace at a temperature ranging from about 7° C. to about 377° C.depending on the reactivity of the carbonyl group.

The condensation catalyst will generally be a catalyst capable offorming longer chain compounds by linking two molecules through a newcarbon-carbon bond, such as a basic catalyst, a multi-functionalcatalyst having both acid and base functionalities, or either type ofcatalyst also comprising an optional metal functionality. In anembodiment, the multi-functional catalyst may be a catalyst having botha strong acid and a strong base functionalities. In an embodiment, aldolcatalysts may comprise Li, Na, K, Cs, B, Rb, Mg, Ca, Sr, Si, Ba, Al, Zn,Ce, La, Y, Sc, Y, Zr, Ti, hydrotalcite, zinc-aluminate, phosphate,base-treated aluminosilicate zeolite, a basic resin, basic nitride,alloys or any combination thereof. In an embodiment, the base catalystmay also comprise an oxide of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn, Re, Al,Ga, In, Co, Ni, Si, Cu, Zn, Sn, Cd, Mg, P, Fe, or any combinationthereof. In an embodiment, the condensation catalyst comprisesmixed-oxide base catalysts. Suitable mixed-oxide base catalysts maycomprise a combination of magnesium, zirconium, and oxygen, which maycomprise, without limitation: Si—Mg—O, Mg—Ti—O, Y—Mg—O, Y—Zr—O, Ti—Zr—O,Ce—Zr—O, Ce—Mg—O, Ca—Zr—O, La—Zr—O, B—Zr—O, La—Ti—O, B—Ti—O, and anycombinations thereof. Different atomic ratios of Mg/Zr or thecombinations of various other elements constituting the mixed oxidecatalyst may be used ranging from about 0.01 to about 50. In anembodiment, the condensation catalyst may further include a metal oralloys comprising metals, such as Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn,Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Bi, Pb, Os, alloys andcombinations thereof. Such metals may be preferred when adehydrogenation reaction is to be carried out in concert with the aldolcondensation reaction. In an embodiment, preferred Group IA materialsmay include Li, Na, K, Cs and Rb. In an embodiment, preferred Group IIAmaterials may include Mg, Ca, Sr and Ba. In an embodiment, Group IIBmaterials may include Zn and Cd. In an embodiment, Group IIIB materialsmay include Y and La. Basic resins may include resins that exhibit basicfunctionality. The basic catalyst may be self-supporting or adhered toany one of the supports further described below, including supportscontaining carbon, silica, alumina, zirconia, titania, vanadia, ceria,nitride, boron nitride, heteropolyacids, alloys and mixtures thereof.

In one embodiment, the condensation catalyst may be derived from thecombination of MgO and Al₂O₃ to form a hydrotalcite material. Anotherpreferred material contains ZnO and Al₂O₃ in the form of a zincaluminate spinel. Yet another preferred material is a combination ofZnO, Al₂O₃, and CuO. Each of these materials may also contain anadditional metal function provided by a Group VIIIB metal, such as Pd orPt. Such metals may be preferred when a dehydrogenation reaction is tobe carried out in concert with the aldol condensation reaction. In oneembodiment, the basic catalyst may be a metal oxide containing Cu, Ni,Zn, V, Zr, or mixtures thereof. In another embodiment, the basiccatalyst may be a zinc aluminate metal containing Pt, Pd Cu, Ni, ormixtures thereof.

In some embodiments, a base-catalyzed condensation reaction may beperformed using a condensation catalyst with both an acidic and basicfunctionality. The acid-aldol condensation catalyst may comprisehydrotalcite, zinc-aluminate, phosphate, Li, Na, K, Cs, B, Rb, Mg, Si,Ca, Sr, Ba, Al, Ce, La, Sc, Y, Zr, Ti, Zn, Cr, or any combinationthereof. In further embodiments, the acid-base catalyst may also includeone or more oxides from the group of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn,Re, Al, Ga, In, Fe, Co, Ir, Ni, Si, Cu, Zn, Sn, Cd, P, and combinationsthereof. In an embodiment, the acid-base catalyst may include a metalfunctionality provided by Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga,In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, alloys or combinationsthereof. In one embodiment, the catalyst further includes Zn, Cd orphosphate. In one embodiment, the condensation catalyst may be a metaloxide containing Pd, Pt, Cu or Ni, and even more preferably an aluminateor zirconium metal oxide containing Mg and Cu, Pt, Pd or Ni. Theacid-base catalyst may also include a hydroxyapatite (HAP) combined withany one or more of the above metals. The acid-base catalyst may beself-supporting or adhered to any one of the supports further describedbelow, including supports containing carbon, silica, alumina, zirconia,titania, vanadia, ceria, nitride, boron nitride, heteropolyacids, alloysand mixtures thereof.

In an embodiment, the condensation catalyst may also include zeolitesand other microporous supports that contain Group IA compounds, such asLi, NA, K, Cs and Rb. Preferably, the Group IA material may be presentin an amount less than that required to neutralize the acidic nature ofthe support. A metal function may also be provided by the addition ofgroup VIIIB metals, or Cu, Ga, In, Zn or Sn. In one embodiment, thecondensation catalyst may be derived from the combination of MgO andAl₂O₃ to form a hydrotalcite material. Another preferred material maycontain a combination of MgO and ZrO₂, or a combination of ZnO andAl₂O₃. Each of these materials may also contain an additional metalfunction provided by copper or a Group VIIIB metal, such as Ni, Pd, Pt,or combinations of the foregoing.

The condensation catalyst may be self-supporting (i.e., the catalystdoes not need another material to serve as a support), or may require aseparate support suitable for suspending the catalyst in the reactantstream. One exemplary support is silica, especially silica having a highsurface area (greater than 100 square meters per gram), obtained bysol-gel synthesis, precipitation, or fuming. In other embodiments,particularly when the condensation catalyst is a powder, the catalystsystem may include a binder to assist in forming the catalyst into adesirable catalyst shape. Applicable forming processes may includeextrusion, pelletization, oil dropping, or other known processes. Zincoxide, alumina, and a peptizing agent may also be mixed together andextruded to produce a formed material. After drying, this material maybe calcined at a temperature appropriate for formation of thecatalytically active phase. Other catalyst supports as known to onehaving ordinary skill in the art may also be used.

In some embodiments, a dehydration catalyst, a dehydrogenation catalyst,and the condensation catalyst may be present in the same reactor as thereaction conditions overlap to some degree. In these embodiments, adehydration reaction and/or a dehydrogenation reaction may occursubstantially simultaneously with the condensation reaction. In someembodiments, a catalyst may comprise active sites for a dehydrationreaction and/or a dehydrogenation reaction in addition to a condensationreaction. For example, a catalyst may comprise active metals for adehydration reaction and/or a dehydrogenation reaction along with acondensation reaction at separate sites on the catalyst or as alloys.Suitable active elements may comprise any of those listed above withrespect to the dehydration catalyst, dehydrogenation catalyst, and thecondensation catalyst. Alternately, a physical mixture of dehydration,dehydrogenation, and condensation catalysts may be employed. While notintending to be limited by theory, it is believed that using acondensation catalyst comprising a metal and/or an acid functionalitymay assist in pushing the equilibrium limited aldol condensationreaction towards completion. Advantageously, this may be used to effectmultiple condensation reactions with dehydration and/or dehydrogenationof intermediates, in order to form (via condensation, dehydration,and/or dehydrogenation) higher molecular weight oligomers as desired toproduce jet or diesel fuel.

The specific ≧C₄ compounds produced in the condensation reaction maydepend on various factors, including, without limitation, the type ofoxygenated intermediates in the reactant stream, condensationtemperature, condensation pressure, the reactivity of the catalyst, andthe flow rate of the reactant stream. In general, the condensationreaction may be carried out at a temperature at which the thermodynamicsof the proposed reaction are favorable. For condensed phase liquidreactions, the pressure within the reactor must be sufficient tomaintain at least a portion of the reactants in the condensed liquidphase at the reactor inlet. For vapor phase reactions, the reactionshould be carried out at a temperature where the vapor pressure of theoxygenates is at least about 0.1 bar, and the thermodynamics of thereaction are favorable. The condensation temperature will vary dependingupon the specific oxygenated intermediates used, but may generally rangebetween about 75° C. and about 500° C. for reactions taking place in thevapor phase, and more preferably range between about 125° C. and about450° C. For liquid phase reactions, the condensation temperature mayrange between about 5° C. and about 475° C., and the condensationpressure may range between about 0.01 bar and about 100 bar. Preferably,the condensation temperature may range between about 15° C. and about300° C., or between about 15° C. and 250° C.

Varying the factors above, as well as others, will generally result in amodification to the specific composition and yields of the ≧C₄compounds. For example, varying the temperature and/or pressure of thereactor system, or the particular catalyst formulations, may result inthe production of ≧C₄ alcohols and/or ketones instead of ≧C₄hydrocarbons. The ≧C₄ hydrocarbon product may also contain a variety ofolefins, and alkanes of various sizes (typically branched alkanes).Depending upon the condensation catalyst used, the hydrocarbon productmay also include aromatic and cyclic hydrocarbon compounds. The ≧C₄hydrocarbon product may also contain undesirably high levels of olefins,which may lead to coking or deposits in combustion engines, or otherundesirable hydrocarbon products. In such cases, the hydrocarbons mayoptionally be hydrogenated to reduce the ketones to alcohols andhydrocarbons, while the alcohols and olefinic hydrocarbons may bereduced to alkanes, thereby forming a more desirable hydrocarbon producthaving reduced levels of olefins, aromatics or alcohols.

The condensation reactions may be carried out in any reactor of suitabledesign, including continuous-flow, batch, semi-batch or multi-systemreactors, without limitation as to design, size, geometry, flow rates,and the like. The reactor system may also use a fluidized catalytic bedsystem, a swing bed system, fixed bed system, a moving bed system, or acombination of the above. In some embodiments, bi-phasic (e.g.,liquid-liquid) and tri-phasic (e.g., liquid-liquid-solid) reactors maybe used to carry out the condensation reactions.

In a continuous flow system, the reactor system may include an optionaldehydrogenation bed adapted to produce dehydrogenated oxygenatedintermediates, an optional dehydration bed adapted to produce dehydratedoxygenated intermediates, and a condensation bed adapted to produce ≧C₄compounds from the oxygenated intermediates. The dehydrogenation bed maybe configured to receive the reactant stream and produce the desiredoxygenated intermediates, which may have an increase in the amount ofcarbonyl-containing compounds. The dehydration bed may be configured toreceive the reactant stream and produce the desired oxygenatedintermediates. The condensation bed may be configured to receive theoxygenated intermediates for contact with the condensation catalyst andproduction of the desired ≧C₄ compounds. For systems with one or morefinishing steps, an additional reaction bed for conducting the finishingprocess or processes may be included after the condensation bed.

In an embodiment, the optional dehydration reaction, the optionaldehydrogenation reaction, the optional ketonization reaction, theoptional ring opening reaction, and the condensation reaction catalystbeds may be positioned within the same reactor vessel or in separatereactor vessels in fluid communication with each other. Each reactorvessel preferably may include an outlet adapted to remove the productstream from the reactor vessel. For systems with one or more finishingsteps, the finishing reaction bed or beds may be within the same reactorvessel along with the condensation bed or in a separate reactor vesselin fluid communication with the reactor vessel having the condensationbed.

In an embodiment, the reactor system also may include additional outletsto allow for the removal of portions of the reactant stream to furtheradvance or direct the reaction to the desired reaction products, and toallow for the collection and recycling of reaction byproducts for use inother portions of the system. In an embodiment, the reactor system alsomay include additional inlets to allow for the introduction ofsupplemental materials to further advance or direct the reaction to thedesired reaction products, and to allow for the recycling of reactionbyproducts for use in other reactions.

In an embodiment, the reactor system also may include elements whichallow for the separation of the reactant stream into differentcomponents which may find use in different reaction schemes or to simplypromote the desired reactions. For instance, a separator unit, such as aphase separator, extractor, purifier or distillation column, may beinstalled prior to the condensation step to remove water from thereactant stream for purposes of advancing the condensation reaction tofavor the production of higher hydrocarbons. In an embodiment, aseparation unit may be installed to remove specific intermediates toallow for the production of a desired product stream containinghydrocarbons within a particular carbon number range, or for use as endproducts or in other systems or processes. The condensation reaction mayproduce a broad range of compounds with carbon numbers ranging from C₄to C₃₀ or greater. Exemplary compounds may include, for example, ≧C₄alkanes, ≧C₄ alkenes, ≧C₅ cycloalkanes, ≧C₅ cycloalkenes, aryls, fusedaryls, ≧C₄ alcohols, ≧C₄ ketones, and mixtures thereof. The ≧C₄ alkanesand ≧C₄ alkenes may range from 4 to about 30 carbon atoms (i.e. C₄-C₃₀alkanes and C₄-C₃₀ alkenes) and may be branched or straight chainalkanes or alkenes. The ≧C₄ alkanes and ≧C₄ alkenes may also includefractions of C₇-C₁₄, C₁₂-C₂₄ alkanes and alkenes, respectively, with theC₇-C₁₄ fraction directed to jet fuel blends, and the C₁₂-C₂₄ fractiondirected to diesel fuel blends and other industrial applications.Examples of various ≧C₄ alkanes and ≧C₄ alkenes may include, withoutlimitation, butane, butene, pentane, pentene, 2-methylbutane, hexane,hexene, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane,2,3-dimethylbutane, heptane, heptene, octane, octene,2,2,4,-trimethylpentane, 2,3-dimethyl hexane, 2,3,4-trimethylpentane,2,3-dimethylpentane, nonane, nonene, decane, decene, undecane, undecene,dodecane, dodecene, tridecane, tridecene, tetradecane, tetradecene,pentadecane, pentadecene, hexadecane, hexadecene, heptyldecane,heptyldecene, octyldecane, octyldecene, nonyldecane, nonyldecene,eicosane, eicosene, uneicosane, uneicosene, doeicosane, doeicosene,trieicosane, trieicosene, tetraeicosane, tetraeicosene, and isomersthereof.

The ≧C₅ cycloalkanes and ≧C₅ cycloalkenes may have from 5 to about 30carbon atoms and may be unsubstituted, mono-substituted ormulti-substituted. In the case of mono-substituted and multi-substitutedcompounds, the substituted group may include a branched ≧C₃ alkyl, astraight chain ≧C₁ alkyl, a branched ≧C₃ alkylene, a straight chain ≧C₁alkylene, a straight chain ≧C₂ alkylene, an aryl group, or a combinationthereof. In one embodiment, at least one of the substituted groups mayinclude a branched C₃-C₁₂ alkyl, a straight chain C₁-C₁₂ alkyl, abranched C₃-C₁₂ alkylene, a straight chain C₁-C₁₂ alkylene, a straightchain C₂-C₁₂ alkylene, an aryl group, or a combination thereof. In yetanother embodiment, at least one of the substituted groups may include abranched C₃-C₄ alkyl, a straight chain C₁-C₄ alkyl, a branched C₃-C₄alkylene, a straight chain C₁-C₄ alkylene, a straight chain C₂-C₄alkylene, an aryl group, or any combination thereof. Examples ofdesirable ≧C₅ cycloalkanes and ≧C₅ cycloalkenes may include, withoutlimitation, cyclopentane, cyclopentene, cyclohexane, cyclohexene,methylcyclopentane, methylcyclopentene, ethylcyclopentane,ethylcyclopentene, ethylcyclohexane, ethylcyclohexene, and isomersthereof.

Aryl groups contain an aromatic hydrocarbon in either an unsubstituted(phenyl), mono-substituted or multi-substituted form. In the case ofmono-substituted and multi-substituted compounds, the substituted groupmay include a branched ≧C₃ alkyl, a straight chain ≧C₁ alkyl, a branched≧C₃ alkylene, a straight chain ≧C2 alkylene, a phenyl group, or acombination thereof. In one embodiment, at least one of the substitutedgroups may include a branched C₃-C₁₂ alkyl, a straight chain C₁-C₁₂alkyl, a branched C₃-C₁₂ alkylene, a straight chain C₂-C₁₂ alkylene, aphenyl group, or any combination thereof. In yet another embodiment, atleast one of the substituted groups may include a branched C₃-C₄ alkyl,a straight chain C₁-C₄ alkyl, a branched C₃-C₄ alkylene, a straightchain C₂-C₄ alkylene, a phenyl group, or any combination thereof.Examples of various aryl compounds may include, without limitation,benzene, toluene, xylene (dimethylbenzene), ethyl benzene, para-xylene,meta-xylene, ortho-xylene, and C9 aromatics.

Fused aryls contain bicyclic and polycyclic aromatic hydrocarbons, ineither an unsubstituted, mono-substituted or multi-substituted form. Inthe case of mono-substituted and multi-substituted compounds, thesubstituted group may include a branched ≧C₃ alkyl, a straight chain ≧C₁alkyl, a branched ≧C₃ alkylene, a straight chain ≧C₂ alkylene, a phenylgroup, or a combination thereof. In another embodiment, at least one ofthe substituted groups may include a branched C₃-C₄ alkyl, a straightchain C₁-C₄ alkyl, a branched C₃-C₄ alkylene, a straight chain C₂-C₄alkylene, a phenyl group, or any combination thereof. Examples ofvarious fused aryls may include, without limitation, naphthalene,anthracene, tetrahydronaphthalene, and decahydronaphthalene, indane,indene, and isomers thereof.

The moderate fractions, such as C₇-C₁₄, may be separated for jet fuel,while heavier fractions, such as C₁₂-C₂₄, may be separated for dieseluse. The heaviest fractions may be used as lubricants or cracked toproduce additional gasoline and/or diesel fractions. The ≧C₄ compoundsmay also find use as industrial chemicals, whether as an intermediate oran end product. For example, the aryls toluene, xylene, ethylbenzene,para-xylene, meta-xylene, and ortho-xylene may find use as chemicalintermediates for the production of plastics and other products.Meanwhile, C₉ aromatics and fused aryls, such as naphthalene,anthracene, tetrahydronaphthalene, and decahydronaphthalene, may finduse as solvents in industrial processes.

In an embodiment, additional processes may be used to treat the fuelblend to remove certain components or further conform the fuel blend toa diesel or jet fuel standard. Suitable techniques may includehydrotreating to reduce the amount of or remove any remaining oxygen,sulfur, or nitrogen in the fuel blend. The conditions for hydrotreatinga hydrocarbon stream are known to one of ordinary skill in the art.

In an embodiment, hydrogenation may be carried out in place of or afterthe hydrotreating process to saturate at least some olefinic bonds. Insome embodiments, a hydrogenation reaction may be carried out in concertwith the aldol condensation reaction by including a metal functionalgroup with the aldol condensation catalyst. Such hydrogenation may beperformed to conform the fuel blend to a specific fuel standard (e.g., adiesel fuel standard or a jet fuel standard). The hydrogenation of thefuel blend stream may be carried out according to known procedures,either with the continuous or batch method. The hydrogenation reactionmay be used to remove remaining carbonyl groups and/or hydroxyl groups.In such cases, any of the hydrogenation catalysts described above may beused. In general, the finishing step may be carried out at finishingtemperatures ranging between about 80° C. and about 250° C., andfinishing pressures may range between about 5 bar and about 150 bar. Inone embodiment, the finishing step may be conducted in the vapor phaseor liquid phase, and use, external hydrogen, recycled hydrogen, orcombinations thereof, as necessary.

In an embodiment, isomerization may be used to treat the fuel blend tointroduce a desired degree of branching or other shape selectivity to atleast some components in the fuel blend. It may also be useful to removeany impurities before the hydrocarbons are contacted with theisomerization catalyst. The isomerization step may comprise an optionalstripping step, wherein the fuel blend from the oligomerization reactionmay be purified by stripping with water vapor or a suitable gas such aslight hydrocarbon, nitrogen or hydrogen. The optional stripping step maybe carried out in a countercurrent manner in a unit upstream of theisomerization catalyst, wherein the gas and liquid are contacted witheach other, or before the actual isomerization reactor in a separatestripping unit utilizing countercurrent principle.

After the optional stripping step the fuel blend may be passed to areactive isomerization unit comprising one or more catalyst beds. Thecatalyst beds of the isomerization unit may operate either in co-currentor countercurrent manner. In the isomerization unit, the pressure mayvary between about 20 bar to about 150 bar, preferably between about 20bar to about 100 bar, the temperature ranging between about 195° C. andabout 500° C., preferably between about 300° C. and about 400° C. In theisomerization unit, any isomerization catalyst known in the art may beused. In some embodiments, suitable isomerization catalysts may containmolecular sieve and/or a metal from Group VII and/or a carrier. In anembodiment, the isomerization catalyst may contain SAPO-11 or SAPO41 orZSM-22 or ZSM-23 or ferrierite and Pt, Pd or Ni and Al₂O₃ or SiO₂.Typical isomerization catalysts are, for example, Pt/SAPO-11/Al₂O₃,Pt/ZSM-22/Al₂O₃, Pt/ZSM-23/Al₂O₃ and Pt/SAPO-11/SiO₂.

Other factors, such as the concentration of water or undesiredoxygenated intermediates, may also effect the composition and yields ofthe ≧C₄ compounds, as well as the activity and stability of thecondensation catalyst. In such cases, the process may include adewatering step that removes a portion of the water prior to thecondensation reaction and/or the optional dehydration reaction, or aseparation unit for removal of the undesired oxygenated intermediates.For instance, a separator unit, such as a phase separator, extractor,purifier or distillation column, may be installed prior to thecondensation reactor so as to remove a portion of the water from thereactant stream containing the oxygenated intermediates. A separationunit may also be installed to remove specific oxygenated intermediatesto allow for the production of a desired product stream containinghydrocarbons within a particular carbon range, or for use as endproducts or in other systems or processes.

Thus, in one embodiment, the fuel blend produced by the processesdescribed herein is a hydrocarbon mixture that meets the requirementsfor jet fuel (e.g., conforms with ASTM D1655). In another embodiment,the product of the processes described herein is a hydrocarbon mixturethat comprises a fuel blend meeting the requirements for a diesel fuel(e.g., conforms with ASTM D975).

In another embodiment, a fuel blend comprising gasoline hydrocarbons(i.e., a gasoline fuel) may be produced. “Gasoline hydrocarbons” referto hydrocarbons predominantly comprising C₅₋₆ hydrocarbons, for example,C₆₋₈ hydrocarbons, and having a boiling point range from 32° C. (90° F.)to about 204° C. (400° F.). Gasoline hydrocarbons may include, but arenot limited to, straight run gasoline, naphtha, fluidized or thermallycatalytically cracked gasoline, VB gasoline, and coker gasoline.Gasoline hydrocarbons content is determined by ASTM Method D2887.

In yet another embodiment, the ≧C₂ olefins may be produced bycatalytically reacting the oxygenated intermediates in the presence of adehydration catalyst at a dehydration temperature and dehydrationpressure to produce a reaction stream comprising the ≧C₂ olefins. The≧C₂ olefins may comprise straight or branched hydrocarbons containingone or more carbon-carbon double bonds. In general, the ≧C₂ olefins maycontain from 2 to 8 carbon atoms, and more preferably from 3 to 5 carbonatoms. In one embodiment, the olefins may comprise propylene, butylene,pentylene, isomers of the foregoing, and mixtures of any two or more ofthe foregoing. In another embodiment, the ≧C₂ olefins may include ≧C₄olefins produced by catalytically reacting a portion of the ≧C₂ olefinsover an olefin isomerization catalyst.

The dehydration catalyst may comprise a member selected from the groupconsisting of an acidic alumina, aluminum phosphate, silica-aluminaphosphate, amorphous silica-alumina, aluminosilicate, zirconia, sulfatedzirconia, tungstated zirconia, tungsten carbide, molybdenum carbide,titania, sulfated carbon, phosphated carbon, phosphated silica,phosphated alumina, acidic resin, heteropolyacid, inorganic acid, and acombination of any two or more of the foregoing. In one embodiment, thedehydration catalyst may further comprise a modifier selected from thegroup consisting of Ce, Y, Sc, La, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, P,B, Bi, and a combination of any two or more of the foregoing. In anotherembodiment, the dehydration catalyst may further comprise an oxide of anelement, the element selected from the group consisting of Ti, Zr, V,Nb, Ta, Mo, Cr, W, Mn, Re, Al, Ga, In, Fe, Co, Ir, Ni, Si, Cu, Zn, Sn,Cd, P, and a combination of any two or more of the foregoing. In yetanother embodiment, the dehydration catalyst may further comprise ametal selected from the group consisting of Cu, Ag, Au, Pt, Ni, Fe, Co,Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy ofany two or more of the foregoing, and a combination of any two or moreof the foregoing.

In yet another embodiment, the dehydration catalyst may comprise analuminosilicate zeolite. In some embodiments, the dehydration catalystmay further comprise a modifier selected from the group consisting ofGa, In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, a lanthanide, and acombination of any two or more of the foregoing. In some embodiments,the dehydration catalyst may further comprise a metal selected from thegroup consisting of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh,Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy of any two or more of theforegoing, and a combination of any two or more of the foregoing.

In another embodiment, the dehydration catalyst may comprise abifunctional pentasil ring-containing aluminosilicate zeolite. In someembodiments, the dehydration catalyst may further comprise a modifierselected from the group consisting of Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P,Sc, Y, Ta, a lanthanide, and a combination of any two or more of theforegoing. In some embodiments, the dehydration catalyst may furthercomprise a metal selected from the group consisting of Cu, Ag, Au, Pt,Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os,an alloy of any two or more of the foregoing, and a combination of anytwo or more of the foregoing.

The dehydration reaction may be conducted at a temperature and pressurewhere the thermodynamics are favorable. In general, the reaction may beperformed in the vapor phase, liquid phase, or a combination of both. Inone embodiment, the dehydration temperature may range between about 100°C. and about 500° C., and the dehydration pressure may range betweenabout 1 bar (absolute) and about 60 bar. In another embodiment, thedehydration temperature may range between about 125° C. and about 450°C. In some embodiments, the dehydration temperature may range betweenabout 150° C. and about 350° C., and the dehydration pressure may rangebetween about 5 bar and about 50 bar. In yet another embodiment, thedehydration temperature may range between about 175° C. and about 325°C.

The ≧C₆ paraffins are produced by catalytically reacting ≧C₂ olefinswith a stream of ≧C₄ isoparaffins in the presence of an alkylationcatalyst at an alkylation temperature and alkylation pressure to producea product stream comprising ≧C₆ paraffins. The ≧C₄ isoparaffins mayinclude alkanes and cycloalkanes having 4 to 7 carbon atoms, such asisobutane, isopentane, naphthenes, and higher homologues having atertiary carbon atom (e.g., 2-methylbutane and 2,4-dimethylpentane),isomers of the foregoing, and mixtures of any two or more of theforegoing. In one embodiment, the stream of ≧C₄ isoparaffins maycomprise internally generated ≧C₄ isoparaffins, external ≧C₄isoparaffins, recycled ≧C₄ isoparaffins, or combinations of any two ormore of the foregoing.

The ≧C₆ paraffins may be branched paraffins, but may also include normalparaffins. In one version, the ≧C₆ paraffins may comprise a memberselected from the group consisting of a branched C₆₋₁₀ alkane, abranched C₆ alkane, a branched C₇ alkane, a branched C₈ alkane, abranched C₉ alkane, a branched C₁₀ alkane, or a mixture of any two ormore of the foregoing. In one version, the ≧C₆ paraffins may include,for example, dimethylbutane, 2,2-dimethylbutane, 2,3-dimethylbutane,methylpentane, 2-methylpentane, 3-methylpentane, dimethylpentane,2,3-dimethylpentane, 2,4-dimethylpentane, methylhexane,2,3-dimethylhexane, 2,3,4-trimethylpentane, 2,2,4-trimethylpentane,2,2,3-trimethylpentane, 2,3,3-trimethylpentane, dimethylhexane, ormixtures of any two or more of the foregoing.

The alkylation catalyst may comprise a member selected from the group ofsulfuric acid, hydrofluoric acid, aluminum chloride, boron trifluoride,solid phosphoric acid, chlorided alumina, acidic alumina, aluminumphosphate, silica-alumina phosphate, amorphous silica-alumina,aluminosilicate, aluminosilicate zeolite, zirconia, sulfated zirconia,tungstated zirconia, tungsten carbide, molybdenum carbide, titania,sulfated carbon, phosphated carbon, phosphated silica, phosphatedalumina, acidic resin, heteropolyacid, inorganic acid, and a combinationof any two or more of the foregoing. The alkylation catalyst may alsoinclude a mixture of a mineral acid with a Friedel-Crafts metal halide,such as aluminum bromide, and other proton donors.

In one embodiment, the alkylation catalyst may comprise analuminosilicate zeolite. In some embodiments, the alkylation catalystmay further comprise a modifier selected from the group consisting ofGa, In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, a lanthanide, and acombination of any two or more of the foregoing. In some embodiments,the alkylation catalyst may further comprise a metal selected from thegroup consisting of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh,Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, an alloy of any two or more of theforegoing, and a combination of any two or more of the foregoing.

In another embodiment, the alkylation catalyst may comprise abifunctional pentasil ring-containing aluminosilicate zeolite. In someembodiments, the alkylation catalyst may further comprise a modifierselected from the group consisting of Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P,Sc, Y, Ta, a lanthanide, and a combination of any two or more of theforegoing. In some embodiments, the alkylation catalyst may furthercomprise a metal selected from the group consisting of Cu, Ag, Au, Pt,Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os,an alloy of any two or more of the foregoing, and a combination of anytwo or more of the foregoing. In one version, the dehydration catalystand the alkylation catalyst may be atomically identical.

The alkylation reaction may be conducted at a temperature where thethermodynamics are favorable. In general, the alkylation temperature mayrange between about −20° C. and about 300° C., and the alkylationpressure may range between about 1 bar (absolute) and about 80 bar. Insome embodiments, the alkylation temperature may range between about100° C. and about 300° C. In another version, the alkylation temperaturemay range between about 0° C. and about 100° C. In yet otherembodiments, the alkylation temperature may range between about 0° C.and about 50° C. In still other embodiments, the alkylation temperaturemay range between about 70° C. and about 250° C., and the alkylationpressure may range between about 5 bar and about 80 bar. In oneembodiment, the alkylation catalyst may comprise a mineral acid or astrong acid. In another embodiment, the alkylation catalyst may comprisea zeolite and the alkylation temperature may be greater than about 100°C.

In an embodiment, an olefinic oligomerization reaction may conducted.The oligomerization reaction may be carried out in any suitable reactorconfiguration. Suitable configurations may include, but are not limitedto, batch reactors, semi-batch reactors, or continuous reactor designssuch as, for example, fluidized bed reactors with external regenerationvessels. Reactor designs may include, but are not limited to tubularreactors, fixed bed reactors, or any other reactor type suitable forcarrying out the oligomerization reaction. In an embodiment, acontinuous oligomerization process for the production of diesel and jetfuel boiling range hydrocarbons may be carried out using anoligomerization reactor for contacting an olefinic feed streamcomprising short chain olefins having a chain length of from 2 to 8carbon atoms with a zeolite catalyst under elevated temperature andpressure so as to convert the short chain olefins to a fuel blend in thediesel boiling range. The oligomerization reactor may be operated atrelatively high pressures of about 20 bar to about 100 bar, andtemperatures ranging between about 150° C. and about 300° C., preferablybetween about 200° C. to 250° C.

The resulting oligomerization stream results in a fuel blend that mayhave a wide variety of products including products comprising C₅ to C₂₄hydrocarbons. Additional processing may be used to obtain a fuel blendmeeting a desired standard. An initial separation step may be used togenerate a fuel blend with a narrower range of carbon numbers. In anembodiment, a separation process such as a distillation process may beused to generate a fuel blend comprising C₁₂ to C₂₄ hydrocarbons forfurther processing. The remaining hydrocarbons may be used to produce afuel blend for gasoline, recycled to the oligomerization reactor, orused in additional processes. For example, a kerosene fraction may bederived along with the diesel fraction and may either be used as anilluminating paraffin, as a jet fuel blending component in conventionalcrude or synthetic derived jet fuels, or as reactant (especially C₁₀ toC₁₃ fraction) in the process to produce LAB (Linear Alkyl Benzene). Thenaphtha fraction, after hydroprocessing, may be routed to a thermalcracker for the production of ethylene and propylene or routed to acatalytic cracker to produce ethylene, propylene, and gasoline.

Additional processes may be used to treat the fuel blend to removecertain components or further conform the fuel blend to a diesel or jetfuel standard. Suitable techniques may include hydrotreating to removeany remaining oxygen, sulfur, or nitrogen in the fuel blend.Hydrogenation may be carried after the hydrotreating process to saturateat least some olefinic bonds. Such hydrogenation may be performed toconform the fuel blend to a specific fuel standard (e.g., a diesel fuelstandard or a jet fuel standard). The hydrogenation step of the fuelblend stream may be carried out according to the known procedures, in acontinuous of batchwise manner.

To facilitate a better understanding of the present invention, thefollowing examples of preferred embodiments are given. In no way shouldthe following examples be read to limit, or to define, the scope of theinvention.

EXAMPLES Example 1 Flow of Hydrolysate from Digestion of CellulosicBiomass in the Presence of a Filter without Backflushing

Example 1A: A microflow digestion unit was constructed from ½-inchdiameter by 1-foot long 316 stainless steel tubing, which was heated viaan electric band heater (Gaumer Company, Inc.), and packed with 4.82grams of nominal ⅛-inch by ¼-inch by 3-mm pine wood mini-chips (moisturecontent of 14% as determined by overnight drying in a vacuum oven at 80°C.). A digestion solvent comprising 20 wt. % 2-propanol, 25 wt. %ethanol, 2 wt. % dimethylketone, and 2 wt. % acetic acid in deionizedwater was prepared and buffered to pH 5.5 using 1N KOH. The buffereddigestion solvent was fed to the digestion unit using an HPLC pump(Eldex). An in-line filter (Swagelok, 10 micron) was placed between thedigestion unit and a high pressure product collection vessel forcollecting effluent from the digestion unit. The digestion unit andproduct collection vessel were pressurized to 1000 psi with hydrogen andheated to 240° C., and digestion solvent flow was initiated at a flowrate of 0.1 mL/min using the HPLC pump. The HPLC pump outlet pressurerapidly increased to exceed the 1500 psi safety limit after less than 3hours of operation., and solvent flow was terminated due to HPLC pumpshutdown. Only 13.2 grams of effluent were collected in the productcollection vessel prior to shutdown. The digestion unit outlet line andthe filter were both found to be plugged with solid wood particulatesfrom the digestion unit. The particulates had a particle size of lessthan 1-mm. Example 1B: Example 1A was repeated with 5.487 grams of pinemini-chips at a digestion unit temperature of 210° C. Overpressure andpump shutdown occurred after 4.7 hours of flow. Example 1C: Example 1Awas repeated with 4.22-grams of pine mini-chips at a digestion unittemperature of 190° C. Overpressure triggered a pump shutdown after 4.8hours, during which time 34 grams of effluent were collected. Thisamount of effluent corresponds to a throughput of only 8 grams ofeffluent per dry gram of wood feed. Example 1D: Example 1A was repeatedwith 4.91 grams of pine mini-chips at a digestion unit temperature of190° C. for 2 hours, followed by 240° C. thereafter. Overpressureoccurred after 5.1 hours, during which time 31.8 grams of effluent werecollected (7.5 grams of effluent per dry gram of wood feed).

Example 2 Flow of Hydrolysate from Digestion of Cellulosic Biomass inthe Presence of a Filter with Backflushing

Example 2A: A 6 gram bed of AX-200 alumina catalyst support (CriterionInc, 1/16-inch diameter extrudates) was placed between the outlet of thedigestion unit and the in-line filter. A sample valve was added betweenthe digestion unit and the fixed-bed filter, which allowed periodicbackflush of the fixed-bed filter to take place. Digestion was conductedsimilarly to Example 1A, with the following exceptions. 4.29 grams ofpine mini-chips were fed to the digestion unit, which was heated at 180°C. for 2 hours, followed by 240° C. for 10 hours. During this time, thefixed-bed filter was backflushed every 2-3 hours by purging 1-3 grams ofliquid and solids from the fixed-bed filter. Supply of hydrogen to theproduct vessel at 1000 psi provided the pressure for backflush. Theliquid pressure at the HPLC pump outlet remained less than 1020 psi, fora digestion unit and product collection vessel maintained at 980-1000psi. No overpressure or automated shut down was observed during theexperiment time, indicating an absence of pressure spikes to greaterthan 1500 psi. More than 166 grams of effluent were collected (44 gramsof effluent per dry gram of wood feed). Example 2B: Example 2A wasrepeated under the same conditions with 4.29 grams of pine mini-chips.Flow was continued for 70 hours, and 261 grams of effluent werecollected. No HPLC pump overpressure occurred during the test period.

Example 3 Flow of Hydrolysate from Digestion of Cellulosic Biomass inthe Presence of a Gravity Separation Unit

Example 3A: The system of Example 2A was prepared, except a 15 inchriser tube was connected to the digestion unit. The fixed-bed filter wasomitted. The riser tube allowed solids and effluent to be isolatedbefore entering the in-line filter. Three experiments were conductedusing 4.43, 4.51, and 4.75 grams of pine mini-chips at a digestionsolvent flowrate of 0.15 ml/min. Under these conditions, 51, 42, and 41grams of effluent were collected without plugging of the in-line filteroccurring or excessive pressure rises occurring at the HPLC pump.Samples from the riser were drained into 8 dram vials in 12-14 gramaliquots. Partially digested wood particulates eluted from the digestionunit gravity settled in the vials within about 15 minutes. Smaller flocmaterial (e.g., less than 100 microns in size) formed upon cooling theeffluent, and after 45 minutes to one hour of settling time, only aboutthe top 10% of the effluent became clear, with the remaining 90%remaining opaque from suspended fines. Extended settling for 15 hoursgave a 1-mm layer of black solids at the bottom of a 32 mm layer oftransparent, orange-brown liquid with no turbidity. Centrifugation for10 minutes at 3400 g's (International Equipment Company Model 428) wasused to produce more rapid settling, producing a non-turbid, transparentliquid with a 1-mm bottom layer of solids following centrifugation.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods may also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A method comprising: providing a biomassconversion system that comprises a fluid circulation loop comprising: ahydrothermal digestion unit; a solids separation unit that is in fluidcommunication with an outlet of the hydrothermal digestion unit; whereinthe solids separation unit comprises a plurality of filters; and acatalytic reduction reactor unit that is in fluid communication with anoutlet of the solids separation unit and an inlet of the hydrothermaldigestion unit; providing a cellulosic biomass in the hydrothermaldigestion unit; at least partially digesting the cellulosic biomass inthe hydrothermal digestion unit to form a hydrolysate comprising solublecarbohydrates and cellulosic fines within a liquor phase; flowing theliquor phase through at least one of the filters to sequester thecellulosic fines; and backflushing at least a portion of the cellulosicfines to the hydrothermal digestion unit while the liquor phasecontinues to flow through one or more of the filters to the catalyticreduction reactor unit.
 2. The method of claim 1, further comprising:forming a reaction product in the catalytic reduction reactor unit. 3.The method of claim 2, wherein the reaction product is used to backflushthe cellulosic fines.
 4. The method of claim 1, wherein the fluidcirculation loop is configured such that countercurrent flow isestablished in the hydrothermal digestion unit.
 5. The method of claim1, wherein at least one of the plurality of filters comprises acatalytic filter comprising a solid support and a catalyst that iscapable of activating molecular hydrogen.
 6. The method of claim 5,further comprising: at least partially converting the solublecarbohydrates into a reaction product on the catalytic filter.
 7. Themethod of claim 6, further comprising: further converting the solublecarbohydrates into the reaction product in the catalytic reductionreactor unit.
 8. The method of claim 1, wherein the plurality of filtersare connected in parallel to one another.
 9. The method of claim 1,wherein the plurality of filters are arranged on a rotatable filterarray.
 10. The method of claim 1, further comprising: reversing adirection of fluid flow in the filters being backflushed; and reversinga direction of fluid flow in one or more of the other filters so as tobackflush cellulosic fines therefrom.
 11. The method of claim 1, whereinat least about 60% of the cellulosic biomass, on a dry basis, isdigested to produce hydrolysate.
 12. The method of claim 1, wherein atleast about 90% of the cellulosic biomass, on a dry basis, is digestedto produce hydrolysate.
 13. The method of claim 1, further comprising:converting the hydrolysate into a biofuel.
 14. A method comprising:providing a biomass conversion system that comprises a fluid circulationloop comprising: a hydrothermal digestion unit; a solids separation unitthat is in fluid communication with an outlet of the hydrothermaldigestion unit; wherein the solids separation unit comprises a pluralityof filters; and a catalytic reduction reactor unit that is in fluidcommunication with an outlet of the solids separation unit and an inletof the hydrothermal digestion unit; providing a cellulosic biomass inthe hydrothermal digestion unit; at least partially digesting thecellulosic biomass in the hydrothermal digestion unit to form ahydrolysate comprising soluble carbohydrates and cellulosic fines withina liquor phase; flowing the liquor phase through at least one of thefilters to sequester the cellulosic fines; at least partially convertingthe soluble carbohydrates into a reaction product in the catalyticreduction reactor unit; and backflushing at least a portion of thecellulosic fines to the hydrothermal digestion unit using at least aportion of the reaction product.
 15. The method of claim 14, whereinbackflushing takes place while the liquor phase continues to flowthrough one or more of the filters to the catalytic reduction reactorunit.
 16. The method of claim 14, wherein the fluid circulation loop isconfigured such that countercurrent flow is established in thehydrothermal digestion unit.
 17. The method of claim 14, wherein atleast one of the plurality of filters comprises a catalytic filtercomprising a solid support and a catalyst that is capable of activatingmolecular hydrogen.
 18. The method of claim 17, further comprising: atleast partially converting the soluble carbohydrates into the reactionproduct on the catalytic filter.
 19. The method of claim 14, wherein theplurality of filters are connected in parallel to one another.
 20. Themethod of claim 14, wherein the plurality of filters are arranged on arotatable filter array.
 21. The method of claim 14, further comprising:reversing a direction of fluid flow in the filters being backflushed;and reversing a direction of fluid flow in one or more of the otherfilters so as to backflush cellulosic fines therefrom.
 22. The method ofclaim 14, wherein at least about 60% of the cellulosic biomass, on a drybasis, is digested to produce hydrolysate.
 23. The method of claim 14,wherein at least about 90% of the cellulosic biomass, on a dry basis, isdigested to produce hydrolysate.
 24. The method of claim 14, furthercomprising: converting the hydrolysate into a biofuel.
 25. A biomassconversion system comprising: a fluid circulation loop comprising: ahydrothermal digestion unit; a solids separation unit that is in fluidcommunication with an outlet of the hydrothermal digestion unit; whereinthe solids separation unit comprises a plurality of filters; wherein thefilters are in fluid communication with the fluid circulation loop inboth a forward and a reverse flow direction; and a catalytic reductionreactor unit that is in fluid communication with an outlet of the solidsseparation unit and an inlet of the hydrothermal digestion unit; whereinat least one of the plurality of filters is in fluid communication withan inlet of the catalytic reduction reactor unit.
 26. The biomassconversion system of claim 25, wherein at least one of the plurality offilters is in fluid communication with an outlet of the catalyticreduction reactor unit.
 27. The biomass conversion system of claim 25,wherein the fluid circulation loop is configured to establishcountercurrent flow in the hydrothermal digestion unit.
 28. The biomassconversion system of claim 25, wherein at least one of the plurality offilters comprises a catalytic filter comprising a solid support and acatalyst that is capable of activating molecular hydrogen.
 29. Thebiomass conversion system of claim 25, wherein the plurality of filtersare connected in parallel to one another.
 30. The biomass conversionsystem of claim 25, wherein the plurality of filters are arranged on arotatable filter array.